Solving Holley Sniper High Idle Issues

When you first posted this I had no idea how to respond. But as you see from the recent revision I did above you seem to be having a fixable issue. Please give this a try and let us know how it works!

I can tell you that when things aren't working the way you wanted them to work that nothing beats knowing for-sure that you don't have a fuel supply problem. And the only way to be positive about that is with a gauge.

Unfortunately, the Sniper does not provide an input for an electronic sender so the next best thing is an analog gauge. And Earl's makes a fantastic little 100 PSI gauge. This will let you know at a glance if something is going awry with the fuel pump. (It should be at or near 60 PSI at idle.)

If you rule out a fuel supply issue then we're going to have to gather a few more clues. If you can track specific engine coolant temperatures where the engine stumbles and dies that would be a good place to start. Good luck!

Check the Distributor Tach Connection to the EFI. If the connection is loose it will cause the system to shut fuel off because the signal telling the EFI the motor is turning stops (to prevent excess fuel from being dumped in the motor).

I would continue checking the electrical connections along the fuel supply. I would suspect something is coming loose causing a stop to the EFI system/Fuel flow.

Interesting question. We have never had that problem with any of the units that we have shipped. However, I did have another fellow who contacted me that claims he went through three units before he could get one that would talk between the ECU and the Monitor. Now, in my lifetime of experience with Holley ECU's that seems unlikely, but this guy sounded really sharp and had nothing to gain by convincing me of his dilemma. I think that the more important point is that Holley kept sending him units until everything was working. That is what I really respect about Holley. It's not that they (or any other manufacturer) is 100% perfect. But they are 100% committed to your satisfaction.

If the vendor from whom you bought the system is coming up blank on ideas then don't hesitate to contact Holley's outstanding tech support department directly at 866-464-6553. I would recommend that you call first thing in the morning, as they tend to get quite busy during the day and wait times can get long. Do please let us know what you find out!

I had that problem, right out of the box it would not power up, sent it back in, had defective hand held.

That is certainly not normal! If it is not a problem with the Sniper EFI System itself then it could be an issue with some sort of harmonic involving the fuel pump. I would gladly engage with you to solve this but ultimately you are going to need to go through whomever you purchased the system if a warranty return is in order. Give them a call and if they are unable to provide customer support the contact the Holley tech support line at 1-866-464-6553.

Thank you chris for for getting back to me on this matter.

I'm using russell hi pressure gas line to feed the gas up to the sniper and using the stock steel gas line that use to be the feed line for the carb to return the gas to the tank. Can the return line be an issue?

I have had 2 faulty gpa-4 255 walbro pumps go bad. I' m going to put the 3 rd new pump this coming friday. Due to when the pump i'm using now makes a loud howling noise when it gets ran for awhile and it gets at a 1/4 tank of fuel or less. Hopefully replacing the pump again will resolve both issues

>I'm using russell hi pressure gas line to feed the gas up to the sniper and using the stock steel gas line that use to be the feed line for the carb to return the gas to the tank. Can the return line be an issue?

So far this sounds like an ideal setup.

>I have had 2 faulty gpa-4 255 walbro pumps go bad. I' m going to put the 3rd new pump this coming friday. Due to when the pump i'm using now makes a loud howling noise when it gets ran for awhile and it gets at a 1/4 tank of fuel or less. Hopefully replacing the pump again will resolve both issues

Whoa. This is actually more troubling than the sound you originally described. Genuine Walbro fuel pumps are virtually bullet-proof. Either the Walbro pumps you are getting are not genuine (lots of forgeries being sold) or else you have something that is killing them. Common killers: No filter in front of the pump, reverse wiring, driving with PWM voltage, running at dead-head pressure.

Since it sounds like your pressure is right, and since the Holley system doesn't provide a PWM voltage, that pretty much rules out everything but the lack of a filter. If you've been running a filter then you have to wonder if you have a legitimate Walbro pump.

If you install a new pump and the noise is still coming from the Sniper EFI System then only the dealer who sold you your system can help you. But get that fuel system fixed before going any further.

I'm so glad you found this helpful--that makes my day!

Don't get too concerned about the specific learn percentage. This is more of a bit of a reality check. The learn percentage should gradually decrease to virtually nothing as the map plus learn table begin to get more and more accurate to your specific setup. It will still change a bit with weather changes and when you get into infrequently-used sections of the map, but it's nothing to worry about.

Regarding your idle speed immediately after start-up, that is determined by your Idle Parked Position. As always, I recommend great restraint in changing any of the parameters until a significant amount of learning has taken place. And, while that is happening, make a note of the temperature before you engage the starter, and then the rpm when it starts.

The Idle Parked Position is set on a temperature-based graph like the Idle Speed Curve. Drop the IAC parked position a bit at each temperature point and sort of back into the solution. Don't make any changes more than about 10% and keep the same basic shape as the original (High/flat below 20 degrees, sloped downward up to 180 degress, and then flat again above that.) If you patiently adjust this over the course of days you will get it just right.

Again, glad this is working for you and look forward to a good report in the future!

That is an strange situation. The fuel pressure regulator in the Sniper is fairly simple and not prone to failure, as far as I know.

I believe that you have this problem solved now with your new inline filter/regulator. But I wanted to go ahead and answer this so that it would make sense to someone who might not go that route.

I think the first thing I'd do is try another pressure gauge. They are prone to be inaccurate. Those little 1/8 NPT gauges are pretty inexpensive and generally pretty easy to find locally.

If you confirm that the pressure is indeed 90 PSI you could pull the fuel pressure regulator apart and check it. Be aware that there is a spring behind there and a diaphragm that you don't want to tear. Technically it is a warranty-voiding maneuver so proceed at your own risk. :-) Just don't let the parts go flying. You want to ensure that nothing is hung up in there.

The only thing that I can think of that would cause the fuel pressure to spike when the motor starts is the increased fuel flow at the higher alternator voltage (jumping from 12.0 to 13.5 volts or so.) If the regulator is working correctly and there is no restriction in the return line that should make no difference however.

Sorry I didn't see this on the Holley forum. i would have been happy to answer there. School's out for spring break this week though so I'm covering for employees on vacation. Kind of cuts into forum time. :-)

Glad to hear that things are working well! Keep in mind that at 60 miles the Sniper is still learning so it will continue to improve.

Second, you may have heard the phrase, "correlation is not causation." That applies here because it is so important to realize that just because the IAC is jumping all over the place when you experience this condition, it does not mean that the IAC is causing it. It could be, but that seems unlikely.

Instead, you need to look at the basics. Clearly, something is changing. What would cause the idle to faulter like that? First thing I would check is the fuel pressure. If you haven't installed a Good Mechanical Fuel Pressure Gauge on the inlet of your Sniper, now is the time. Purists will sniff that these are not accurate to the tenth of a PSI. But nothing beats a good solid gut-check when things aren't working and this provides just that. (Plus they it just looks way cool in your engine compartment!) The link above includes the option to buy a -6 AN port that goes right on the inlet of your Sniper and makes installation a breeze.

If your fuel pressure is solid at about 60 PSI then you should start looking at other things that might cause the idle to faulter, but this is a good start. Let me know how it works for you.

The engine ran so good, I would have never suspected the Fuel Pressure to be an issue. However based on your reply I connected the Fuel Pressure gauge and started up the engine. I was shocked to see it at 95lbs!!!

I called Holley today, and before I could even described the symptoms the technical rep said "You ahve high fuel pressure". Yes its at 95lbs, needless to say he promised a new regulator would be in the mail today. He said they have been having an issue with these lately.

Thanks Again for your help. I keep wondering how it was running so good with such high fuel pressure.

Thank you so much for your follow-up. It is good to at least know that the Sniper fuel pressure regulator can have high pressure failure issues (contrary to what I posted to Scott back on April 13th!)

The fact that it ran so (at times) with 90+ PSI fuel pressure is a testimony to the Holley's closed-loop technology. Even though the Sniper's fuel map is programmed to provide the correct amount of fuel via injectors spraying at 60 PSI, if the pressure is jacked up to 90 PSI the wideband sees that you are rich and faster than you can even detect it audibly lowers the duty cycle to inject the correct amount of fuel.

Except at idle. At that point, with 90 PSI of fuel, the ECU can't turn the duty cycle down low enough to idle properly. Strangely, what I've seen is that it idles too lean as the injectors are effectively shut off.

Thanks again for the follow-up and glad to hear that everything is working well now. Enjoy your Sniper!

I know this is old, but I bought and installed a Sniper kit in 9/18. Though it started and ran good, it was dumping fuel and would not lean out to AFR set points. After talking to Holley tech, I replaced the factory regulator and problem solved.The regulator had what appeared to be a film or something almost clear embedded in some of the screen, maybe from factory or from install, but that was my issue.PS : this page and other forums have helped me a lot. Thank you.

That's a nice change of pace--a low idle issue! Fortunately, these are much easier to solve. Simply turn the idle speed screw on the linkage in until the throttle plates open enough for the idle to increase. It won't take much! Maybe give it a half-turn before you start it and then start and tweak. Note that sometimes you can get into a back-and-forth situation. If that happens then follow my 10-step process shown above.

In most cases the IAC (Idle Air Control) circuit is the source of the whistle. Some have suggested the gasket might cause it but I've never heard of anyone fixing the whistle by adjusting the gasket (and many have tried.)

Since this isn't a consistent issue with all Snipers that tells me that different IAC settings tend to make the whistle. So try changing your IAC hold value slightly:

Tuning : Advanced : Adv. Idle : IAC Rampdown : IAC hold position

Change this by maybe 2% in either direction. If you go too high then the motor will not return to your target idle when you come off the throttle. If you go too low then it may stumble or even stall when coming off of throttle. But there are several degrees of play there in which it should still work fine. And, hopefully, within those degrees you will find a place where you don't get the whistle.

Please let us know how this works out for you! :-)

Chris, Thank you for your input. I tried adjusting my IAC up to 10deg in both directions with no change. I have now determined with the TPS the noise correlates with the opening of the secondary butterflies. I watched the butterflies start to open at about 35 on TPS. Does that make sense to you?

It could be that the air flow across the secondaries as they are opening is creating that whistle but that isn't commonly the case.

Did you check for leaks around the gasket of the air cleaner? Those don't impact the way the engine runs and can cause the whistle sound you describe. If you remove the air cleaner entirely and the whistle continues then you can rule that out. Otherwise, if removing the air cleaner eliminates the whistle then try to use a thicker gasket or try lightly greasing the gasket. (Grease can sometimes do the same thing as a more permanent gasket sealer without making the removal of the air cleaner such a pain.)

I have a bone stock 350 that I installed a Sniper on and had the same whistle noise, presumably from air going past the butterflies. I have an adapter on the manifold for squarebore to spreadbore and then a phenolic spacer. I've read that a spacer with 4 individual holes will solve this, but after I installed the progressive linkage the noise went away!! Hope this helps!

Thanks for the input.

I would disregard any correlation between idle control between the Stock and Street/Strip setups. That is likely just confusing the issue.

Instead, choose whichever setup most resembles your camshaft and stick with that. It will learn the fueling eventually either way, it's just that one might get you there a little faster.

If the idle is fine at start-up but then increases after you depress the throttle then you might need to lower your IAC Hold Position a bit. However, I always preach to never touch any of the controls on the handheld until you have a couple hundred miles on the engine in a range of driving situations. But, if the idle is so high that it is making you crazy then you might try dropping that number just a bit. If you drop it too far the engine will stumble or stall when coming off the throttle with the car out of gear, so you'll know when you've gone too far.

What you're experiencing is the delay time between the ECU sensing the additional load and the IAC actually increasing the RPM. Were the additional load a simple step function it would be challenge enough for the ECU to gracefully increase the engine speed without overshooting. Since the load is more of a wave that increases the most initially and then decreases again, the ECU is doing really well to get the idle under control in only two or three over/under shots as you describe.

You don't mention if you have your Sniper ECU controlling timing. If not then I think you are going to find that this will solve much of your problem. The Sniper ECU can use the timing to help maintain the idle speed and that will definitely be useful in that transition from Park/Neutral to Drive.

If you don't have ECU-controlled timing, or if you do and it's not fully compensating, it may be necessary to increase your target idle slightly. Even 50 RPM can make a difference in how much impact the transition to Drive has on the idling engine's ability to stay at a fixed RPM.

I would not recommend it in this situation but anytime a "kick" in idle speed is desired that is easily done by setting the kick value in Tuning > Advanced > Adv. Idle > IAC Kick. This increased idle speed is triggered by grounding the orange wire in the 10-pin I/O harness. This is normally used as an A/C idle-up circuit. Commanding the engine to automatically increase speed when switching into drive is a little scary to me though. :-)

Chris thank you for the info. Yes it is controlling the timing and I had issues at first and it controlled the idle just fine. Now I have most of the bugs worked out it runs fine on the highway and around town it's just the idle. I will turn it up some. I have it set at 650 and it idles anywhere from 590 to 700. Is that normal? I will turn it up some more.

Is this something that the ECU will learn? It has gotten a little better after I drove it for three hours today.

I want to save the Kik because if I get this working good then I would like to add A C and use the kick for it.

Motor is Mopar 360 with mild cam and automatic. MSD pro billet and 6AL box I have heard some guys complain that the idle is too good and they can't hear their cam anymore I'm kind of like that. I guess we can't have everything. And thanks again for taking your time to answer these questions.

Glad to hear that you have timing control enabled, Gary. That is the only way to fly. :-)

Yes, learn impacts idle too, and remember the even when the basic learning is done there will continue to be some learning for changes in weather, altitude, etc.

Go ahead and try a few idle settings and see how they impact the idle-speed searching. It's all part of the pleasure of EFI. Enjoy!

To figure this out it's going to be important to gather a bit more data. What must remain foremost in your mind is that the only thing that can cause the idle to increase is additional air getting into the engine. Once we recognize that, the next step is to narrow down all possible sources of additional air until we discover the cause.

Start by keeping an eye on your IAC number. Get a solid feeling for where it is when the engine is warm and the idle speed is correct. Then, when you experience the high idle, note if the IAC number has increased. The answer will divide the possible sources of additional air into two, greatly simplifying the problem.

If the IAC number has not increased, then review the article above regarding high idle from a vacuum leak or high idle from sticking linkage. If the IAC number is increased during this high idle, review the points about high idle from tuning issues. If this is the case then I would look particularly close at the IAC hold position and IAC ramp start.

Let us know what you find and what works for you!

I've been messing around for a bit trying to eliminate any possible vacuum leaks. The latest was changing the power brake booster.Today I drove it to work and no issues at all. Idle when warm was 850-ish and IAC 3-4 just as when I readjusted it the night before. Coming home from work today it was much warmer and took a little longer due to traffic. By the time I was near home, the idle in Park was 1050, IAC 0. Shut it off and immediately restarted and idle was now 880 with IAC at 8.

If this is a vacuum leak I can't figure out what would cause it to go away immediately after shutting down the car and restarting. The 5-6 times it has happened now have been after the car has been running for at least 20 minutes. I haven't driven it for the 30-40 minutes like the several times it idled at 2200. The last 2 times have been shorter and one time the high idle was around 1400, this time around 1100. Every time though I can turn the car off and restart and it settles at 850 with IAC 2-4.The thing that has me puzzled is how the with the only difference in condition of the car being the restart, the idle is "fixed"Any clues on where to look next please let me know

Well, it sounds to me like your Sniper is doing its best to reduce your idle. As you have noted, each time the idle goes up. your IAC is at zero. Unless you have ignition control enabled, that is the only thing it can do to reduce the idle.

Realize the only things that can cause the car to idle up as you describe are air and ignition advance. If the IAC is zero, and if putting your finger over the IAC port doesn't lower it, then it's not the IAC circuit. It is working fine when you restart the car, controlling idle perfectly at 8 steps open so it is unlikely to fail when the car warms up--or correct itself instantly when you restart it..

So, if you don't have any vacuum leak, and the throttle plates are fully closed, the only thing I can guess is something is causing your ignition timing to change. As inconvenient as it might seem, I'd recommend keeping a timing light handy and checking your timing during the high idle condition and then again after restarting. Your mechanical advance will naturally change the timing a bit but it should be fairly close.

Interesting situation you have. First, recognize that the IAC and the TPS are not inter-related in any way. Though they both are indications of the amount of opening through the throttle body, the TPS is the throttle opening percentage and the IAC number tells us how far the IAC stepper motor is opening the bypass air circuit.

If I understand you correctly you are saying that the TPS reads somewhat normally (traveling from 9% to 100% or so) but that when you cycle the key it once again starts at 9%. That is not something I'd ignore. I'd recommend you contact Holley Tech support to get their input (1-866-464-6553; call early for the shortest wait times.) Having a TPS that won't go lower than 9% will affect the acceleration enrichment correction, and could create a stumble at the first moment of throttle opening.

Yes, the IAC can and will fluctuate depending on changing conditions. That is a good thing.

I don't have a specific target RPM but always encourage automatic transmission users to bias the idle just a tiny bit higher than what you might otherwise. Properly configured, the Sniper does a fantastic job of responding to the transition from Park to Drive. But if the idle is a little bit higher then it doesn't have to jump quite as much in response to the load, and tends to react a little bit more smoothly.

Yes, you are correct. TP range is normal goes up to about 90% with throttle pedal to the floor. I recently detached the TP sensor from the side of the sniper to physically move it and it still would struggle to get to 0%. After manually making the sensor go through the full range a few times, I reinstalled it and now my TP will read anywhere from 0% to 4% when I key on. Usually it wont stay on 0% very long and soon changes to another number like 1 or 2%. The problem I believe this is creating is after I start vehicle (and its still in park), the IAC drops down to my hold percentage of 10% (since throttle % is not 0) before engine is warm and therefore causing the engine to stall out. I've increased the IAC rampdown time to 8 seconds to try to combat this, but wondering if it will correct itself over time or if I need to possibly replace this TP sensor. I also raised idle at Park a bit with the idle screw. As I have it set right now, my idle at park is in the high 700s and my desired idle in gear is set at about 700 cold (80 degrees) and gradually lowers to 590 once engine temp reaches 160 degrees. Drive great and idles perfect at stop signs. Just getting it to act right at startup is a struggle.

Yes, having an accurate TPS is very important at idle. And your understanding of how the throttle position affects idle is exactly correct. And increasing your idle via the idle screw was also a good idea, because that will lower your amount of IAC that is necessary to keep your engine at the target idle speed.

What I can't explain is why your TPS is acting so randomly. That could be a problem with the TPS or it could be some sort of throttle linkage issue. I recommend confirming there is no throttle linkage issue first. With an assistant pressing the accelerator, you need to make sure that when the accelerator is pressed to WOT that the throttle blades are fully opened, and when accelerator is lifted the linkage is fully at rest against the idle speed screw. If either of these is not the case it must be remedied.

After you have done this then you might want to involve Holley Tech Support about the TPS, or it may be easier/faster just to visit the local auto parts store and pick up a new TPS and install it. It is a common one. Worst case you'll have a spare on hand, and if the TPS is faulty you will have solved the mystery.

It could be a couple of things. First, I'm kind of insistent about not changing any of the default settings unless the vehicle absolutely will not cooperate enough to drive/learn, and only then if you have a specific understanding of the problem and a specific solution. If the ECU has not spent some significant time learning yet, I'd recommend going back through the setup wizard and getting everything back to default. (If you do this you will need to reset the -40 degree setting mentioned at the top of this article.)

Take a look at your AFR during the starting process. I have one customer who is having some similar issues and his AFR is down at 9.6:1 when it won't start. He is able to get it to start by quickly depressing the accelerator to at least 60% and releasing. (Do this while you are cranking.) That is the default "Clear Flood" TPS setting and turns all fuel off until the engine cranks. It works instantly for him.

If that fixes your problem then you have a starting place. Again, I would lean on that solution to let the vehicle drive/learn before you try to "fix" anything. You'll be amazed at how much of this just "goes away" when you drive it enough.

First, let me congratulate you on your patience in letting the system learn. I think that a great number of the challenges that Sniper EFI System Owners face are brought on themselves by getting into the control settings before the system has really had a chance to learn.

But I think it is safe to say that you are now at a point were some manual tuning is a good idea. And your question is very perceptive: You must first know whether the bog is a lean or a rich condition before you can make the correct adjustments.

One way is to very carefully watch the handheld monitor, and that may be adequate. But if you can datalog the bog you can know much more precisely what is happening. Plus, you can email that file to me and I can be of more help.

I don't want to go on too long here but once you know if you're trying to add or remove fuel, there are a couple of ways to go. There are six different acceleration enrichment tables that you can tweak and that may be the way to go. But another thing to consider is adjusting your target A/F ratio. And if you're going to go this route I'd recommend that you switch from "Simple" (3 A/F targets, one each for Idle, Cruise, and WOT) and go to the 2-D Table

Once you so this, and after you have your CAN-to-USB harness attached to your laptop with the Sniper software, you can see precisely the cells where the system is operating when the bog occurs. Simply go to those cells, tweak them up or down as required, and the ECU should now be able to learn its way around the bog.

This is a mighty big subject for a blog post reply, I should probably start doing some videos on this. Remember that as an EFI System Pro customer you have access to me at any time via my cell phone. I'm happy to walk you through what is required. Thanks for the great question!

Several good bits here. Let me start with the engine not starting until you press the throttle. Until the engine starts, the throttle only has one purpose: To detect you pressing it to 60%, at which point it shuts off the fuel injectors. That 60% (which is configurable) is known as the Clear Flood TPS. It is how the engineers allow you to clear a flood condition when you detect it. So, if pressing the throttle is making it start, it's because you're flooded.

Which is consistent with your rich idle condition comment, right? But before you adjust the ECU to lean the idle out, first confirm that your fuel pressure is right. The only way to do this is by installing a mechanical fuel pressure gauge. If your fuel pressure regulator has failed (and they often fail by blocking return fuel and maxing your fuel pressure) then it could lead to rich idle, particularly until your engine gets up to temp.

Give that a go and see if you don't make some progress! Then follow all of the instructions above, including confirming the idle speed curve setting at -40 degress as well as following my 10-step process for setting the idle. I think you'll be all set!

Thanks for the info Chris. I think I figured some of my problems out...I'll try to explain. My car will now start when its cold, but after about 30 seconds the idle drops down and begins to run like crap. My car will not idle right until it gets to around 130 -140 degrees. Is there away to program the ecu to compensate for this at start up. Also, I was seriously rich at idle...so rich it hurt your eyes. I figured out I was going the wrong direction when I was messing with the AFR programming. I thought 12.0 was leaner at idle, but I figured out I was wrong....lol. I set the AFR at 13.5 and all is good now.

I managed to get the IAC down to around 0% - 8%...is this good?

Now that you've got your IAC set I'm going to recommend that you run your setup wizard again, which will reset the ECU to the default settings. You will need to change the -40 degree idle speed setting again but I recommend not touching anything else. Only in the unlikely event that your engine simply won't run well enough to drive and self-learn should you consider tweaking anything inside of the first several hundred miles.

I think that this time around you will find that it starts and idles really well and only gets better from there. Try it! :-)

Yes, the sound coming out of your Sniper throttle body is a pulsation from the fuel pump that is pulsing the mechanical fuel pressure regulator. I think that your Sniper system is working fine but would definitely check ouf the fuel pump.

And yes, monitoring the fuel pressure is the right answer. I am extremely suspect of what you were told about the Sniper ECU monitoring fuel pressure, for several reasons. First--besides the fact that it's not represented on the display, it is not even a parameter that you can datalog. Second--even in the HP and Dominator systems where a fuel pressure sensor can be dalogged and displayed, the fuel pressure is not fed back into the algorithm. It is simply for the benefit of the user. And since they really had an insanely-tight monetary and real estate budget in the Sniper EFI System, it is unlikely that the added something that wasn't absolutely necessary--and then forgot to use it..

And you are spot on about the little Earl's gauge with optional -6 AN port. I am at the point where I almost insist that every Sniper EFI System owner purchase one of these. Without it you are working in the dark. Get that thing installed and you're going to know a whole lot more about what's going on.

I've helped folks work through a number of challenges with their Sniper EFI System installations. However, I can't think of a single one that was because of low vacuum. In fact, it is those users who seem to end up most impressed with the system. I'd say make sure you buy from someone who can give you good after-purchase help (hint!) and if you do run into any problems then, yes, the plethora of tunability adjustments available through either the handheld or the Sniper Software will certainly be enough to get you right where you need to be!

The jack-rabbit start can usually be minimized by adjusting the throttle linkage. Ultimately, it is about making the pedal softer, particularly at initial throttle opening. Some suggestions:

• Lubricate the linkage so there isn't as much native resistance.
• Use a softer throttle spring.
• If you have a bellcrank in your throttle linkage, ensure that the linkage is not engaging the bellcrank at an angle greater than 45 degrees at either end of the throw. This may require shortening or lengthening a rod.

i did have the same problem.try lengthening the lever of the throttle.meaning the length from the center of the throttle to the point where you attach your cable or your rod from the peddle.

Hey Tommy, we've got at least one thing in common. I, too, wish you'd bought your Sniper from us! :-D

Still, I hate to leave someone hanging so I'll try to help. Is there any chance that your timing has changed since you installed your Sniper? The very first thing I would do is get ground truth on your timing. It sounds to me like it is way retarded.

In the event that the timing is right then take a look at your AFR--the actual AFR, not the target. It's pretty hard to get the header tubes glowing at idle with a lean AFR. The engine might run hot but if the timing is right it should keep that heat in the engine--which is where the damage turns up. So check that timing and I think that you're going to find you need a good bit of advance.

Now that you've installed at least four Snipers it is going to be imperative that you learn to create and read datalogs. At some point you come upon problems that evade the easy answers and this is a good example. WIthout knowing quite a bit more it will be more than challenging for you to identify the problem and solve it.

Fortunately, Holley provides their amazing Sniper Software. Follow this link to download it for free if you have not already done so. This software is going to allow you to open both the configuration file and the datalogs that you create, overlay them and you can get a much better idea of what is happening.

While it is not mandatory, I recommend the Sniper EFI CAN-to-USB Adapter to move the data between your Sniper EFI and your PC rather than trying to do this via the SD card. For someone in your position, it will become an indispensable tool in your tool box. You might even want to add our 4-foot extension harness that will allow you to connect/disconnect the display or CAN-to-USB adapter from inside the car (rather than trying to do that leaning over the engine and under the breather.

Once you have done this the challenge is to create a datalog that includes the ":snap" you describe. That, I am afraid, is going to involve a little bit of luck if you don't want to create a 250 MB data log. But when you have it then you can look for exactly what the IAC is doing at that point, and if there is anything that might lead to this happening. Learning to install these is great--you're about to embark on the next great adventure of advanced troubleshooting.

Hello, Chris, thanks for the help.

I have not installed the software yet, and I'm having trouble with two cars. I've made all the adjustments, all the settings, and the IAC issue is driving me crazy. Suddenly, the engine accelerates alone, hears a great deal of air being sucked in, and when I close the IAC's hole with his finger, the engine is normal.

The data on the touch screen I see are:

AFR, A / F = 35.6
Target AFR, A / F = 13.5
Cl. Comp. % = 49
IAC Pos.% = 0
TPS% = 1
Duty Cycle% = 3
Pw. Inj. = 2.34
Fuel Flow lb / h = 12.1
RPM = 1200
My slow gear I leave with 650 RPM, the IAC Position I leave between 5 and 6%, the engine works beautiful, the car runs a lot, but suddenly, the engine does that. Turning off and then on again, the engine returns to normal. I've changed all the EFI parts, including the throttle body, and the problem persists.

Please give me a hand. Thank you very much.

The data that you provide shows that you have at least two problems.

You are aware of the idle-up problem. When I see that your TPS is 1%, that tells me that you may have an RFI problem. The Sniper resets the TPS to 0% each time that you key the system on. Now, 1% on the TPS isn't a problem, but when it goes to 2% (which is inevitable if you have RFI moving it to 1%) then the IAC is going to go to it's hold position (30% by default) and the engine is going to rev up. That's what you're seeing.

You're going to have to clean up the wiring in your engine compartment, In particular, look for spark plug wires that might be running near your throttle position sensor. You will have to do this until the TPS stays at 0% when the throttle is closed.

Your second problem should be a bit more concerning. Your AFR is pegged lean. You might have a bad O2 sensor, really bad exhaust leak or a problem with the ECU. Your closed loop compensation is adding a full 50% fuel. You're going to have to get this fixed or it's going to cause even more problems than the high idle. Hang in there--you can do it.

It sounds like you need a bit more of a fuel squirt on acceleration, Brett. There are two ways to address this--you can let the system learn or you can manually adjust the acceleration enrichment. Of the two options, I generally recommend the self-learn.

While you have over 200 miles on the system, you must realize that in the part of the map where the ECU finds itself during lanches you might only have a total of 5-10 seconds in any given cell. These are "transitional" cells, and you really have to make the effort to learn in these areas of the map. What I would recommend is getting somewhere that you can spend a significant amount of time doing starts. Start by doing the fastest start you can that doesn't bog. Then do it just a bit faster--just enough for it to bog a bit. A couple of those and you should feel it getting better. Then a little faster--until bogs at that level work themselves out. I'll bet you find that you can get it working great without any manual tuning.

There's nothing wrong with manual tuning, but at this point that is just compensating for an inadequate fuel map. That is not the way to go. It is always best to get the base map as close as possible before adding acceleration enrichment.

Some advanced concepts...If you have the Sniper Can-Bus to USB Adapter, you can connect your laptop, open the software to the learn table, and get a visual for where in the table you are experiencing the lean bog. (Don't drive and watch--get a helper!) That way you can get into that part of the table that needs tuning, and you can watch your learn numbers grow. Once you've done this, the next natural step is to transfer the learn table to the base map, then go in and smooth out the sharp edges, which are going to be at these transitional states. This will go a long way to improving your fuel map without manually adjusting the acceleration enrichment.

If you use your handheld to go here:

Tuning > Advanced > Adv Idle > IAC Startup

You will find a startup IAC percentage, an amount of time it holds at that percentage, and an amount of time it takes to idle down to the normal idle speed.

By default, that number is 50% at normal operating temperature. You can drop it down and you will find it will behave more like you expect.

You could go either way.. I would not expect that an electric fan would create a noticeable load on the engine but if it did then you'd want to set the idle screw when the fan was not running. If you go the other way then you might find that the IAC zero's out when the fans are off. That is not a huge problem but it just means the IAC has no ability to lower the idle beyond what it is running at that point.

Thanks for your very detailed question! I've abbreviated it just a little bit but am appreciative of the added insight your comments provided.

Off-idle performance can really be a challenge to self-learn but be assured that it can almost always be done. Realize that when you drop the throttle, the engine enters a condition it will only see for a fraction of a second at a time. The manifold pressure increases with the throttle opening but the RPMs are still low. That changes almost instantly as the engine revs.

Since the learning algorithm requires some time exposure to a certain condition to make larger changes, that half-second makes only the smallest impact. It will need to see it again and again. Note too that the larger the throttle stab, the more brief the time in that cell and the more gradual the change.

Here's what I recommend: Get somewhere where you can repeatedly stop and go. Start with the most gradual throttle input you need to launch well, then slightly increase until you feel some stumble. Repeat until that stumble goes away, and then try a bit more throttle. I think you will find that it will learn its way through this.

During after-start idle, the idle will jump up to about 70% if the engine is cold, stay there about 4 seconds and then ramp down to the target idle speed for the current engine temperature.

After the start process, If the idle speed is higher than the target idle then the IAC should begin closing as long as the TPS is below 2%. If the TPS is even just 2%, the IAC will go to the hold position (normally 30%) and will not change until the TPS goes back below 2%.

If you create a datalog you will be better able to confirm if something is not working correctly. If your RPM is 2000, your TPS is 0, and your IAC is not closing, then there is some problem. However, I have never found that to be the case. Please check your process again and see if you can see very specifically what is not working correctly.

Thanks for sharing that, Jason--great info! And so glad you guys are enjoying the Sniper EFI system. We have shipped quite a few of these to customers in Australia and New Zealand so I know that there is becoming a good following there!

We recommend this Inline 10-micron fuel filter to prevent problems like that. It is made by one of the biggest names in fuel filters and sold under the Parts Master label so it is quality and great price in one. It's the same one that Holley puts in their Sniper Master Kits and I've never heard anyone with anything but good things to say about it. Thanks again for your insights!

Throttle Tip-In tuning can be a bit of a challenge but I'm confident you can get this resolved, Mike.

Let me start by saying that unless you've really done a lot of driving on the system in some useful learning situations then I would set this issue aside and not even think about it. Throttle Tip-In puts you in a part of the fuel map where you stay for only milliseconds at a time. It really takes a lot of throttle tip-ins before you get anywhere near "learned" in this part of the fuel map.

Based on your description, it sounds like you have a lean stumble. You are looking in the right area but I would probably not change the ROC blanking. Going in the direction you did (higher) is going to reduce the acceleration fueling that the engine sees. Going lower with the blanking might pay dividends, but there is so little room below 7/8 that you will quickly be in a range where every tiny variation in the TPS or MAP is throwing extra fuel into the engine. Not good.

There isn't set solution here that works for all engines. I would start by datalogging the situation and seeing exactly what your learn table looks like in the area immediately around the tip-in. If it is already adding fuel, it may be worth expanding this into the area where the tip-in is occuring (and where there is no learning occuring.)

Then look a the datalog and find out what TPS ROC and MAP ROC is most likely to cause the problem. Make sure that your blanking level is _below_ that (being careful not to find yourself in the situation I describe above.) Consider adding fuel in the AE vs TPS and/or AE vs MAP ROC tables in the area where the stumble is occuring.

Since this is happening at such low TPS levels it is possible that your engine would prefer a lower (richer) target AFR number at idle. You mentioned going from 13.5 to 14.2 but you'd want to go in the other direction--maybe to 13.2. I would only play with this if you are finding that the other adjustments I suggested aren't working. Good luck!

Yes, let me know how that setup process works. Two things to keep in mind as you do that.

First, recognize that the amount below your target where you set the hard idle will be different on different engines. I had a customer who struggled to understand that. He thought that something was wrong because when he set the idle 50 RPM below his target the resulting IAC postion was far too big. In some cases, you may only be able to put as little as 10 RPM between the hard idle and the target idle. Others might require 60 RPM. You'll have to go back and forth a couple of times to get it just right.

The second thing to realize is that even after you get it just right, you need to keep an eye on the IAC number and reset the idle if it gets outside the 2-8% range when idling when warm. That will happen occasionally, but less as time goes and on and the engine tune stabilizes. It's all part of the adventure!

I am right back to where I started. I have been able to get it pretty close to idle with the IAC between 2% & 12%. When I shut it off then start it back up...the RPMs shoot up to anywhere between 1500 and 2000 and they will not get lower until I turn down the set screw. From here...the cycle continues and I am back to trying to zero down an idle. I did notice that when I thought I had it set that my Air/Fuel ration was 15:1 and I believe the target is 13.5:1.

Based on your situation above as well as some of other experiences, I recognized that I needed to improve my tuning procedures above to better explain what steps to take if that 10-step process doesn't completely solve the problem. Have a look--I think this is going to allow you to fix your idle problem.

Chris...I finally got everything resolved. After speaking with Holley Tech Support and Tech Support from where I purchased the system...they decided to replace it. As soon as I got the new one installed and wired...it fired right up and did everything it was suppose to do with no issues. Bottom line is...my first one must have been faulty. Thanks for all your help Chris!

This may sound crazy but I'm going to jump out on a limb here and say you don't have an idle issue--you have a timing issue. I think that your timing is too retarded. Even though you think your timing is perfect I'd suggest you try cranking about 5-10 degrees of advance into the distributor and just see if that doesn't work better for you.

Remember this: adjustable timing pointers go out of adjustment and harmonic balancers slip. And all too often we don't take that extra step of using a piston stop to ensure that the timing pointer is on zero when the engine is truly and exactly at top dead center. If you find that adding 5-10 degrees of advance helps then it's time to do reconfirm TDC. Then your low idle problem will go away. :-)

I will confirm TDC with balancer but I have had balancer off and timed it before and after with same results. It has a lightweight centrifugal spring kit installed so I reach total timing around 2500 rpm. It’s timed to 36 degrees. If I go any more it will ping. Running the vacuum advance and of course I time it disconnected. I’ve played with the timing on this thing multiple times.

Car was fullly restored last year. Using a Snap-on variable timing light so this is why I say timing is perfect. I’ve also used another snap on light to confirm. Intake has been on and off 3 times no change. 3 different fuel pumps. Ran 2 Holley carbs and an Edelbrock. Always had to set idle above 950. If idle drops below 800 it won’t come back it’ll chug around 300 rpm for a few seconds then die. Duration @.050 is 240 intake 246 exhaust with .574/.578 lift.

I put sniper on in hopes to be able to just turn key and start without fumbling with pedal to keep it going and to correct idle drop when ac kicks on. It drops about 200rpm when clutch engages. Running new vintage air system so the is only a single power wire to compressor that’s why I asked if I needed to run input wire to ac relay or if iac would pick it up fast enough(which it’s not).

I appreciate everything you are saying. But if you will just advance the timing at idle and see if it makes a difference then that will tell you what you need to know. It's not necessary to drive it that way. Just add 5 or 10 degrees of advance and see if it doesn't idle better. If it does then you can put on a heavier spring so the advance doesn't come in as fast, or use a lighter weight.

To be honest, you sound like an ideal candidate for Sniper ECU ignition timing control. You could install the Holley Dual-Sync Distributor and let the Sniper control your timing. The Sniper even has a feature that allows it to use the idle timing to control the idle speed. That disappears as soon as the throttle is pressed and then you immediately revert to your timing table.

You can certainly use the compressor to initate the IAC Kick, but remember that this is just a temporary idle boost to ensure that the engine doesn't die when the AC is first turned on. If the engine will after the 4 seconds that the IAC kick drops off then it's not really going to help.

At any rate, it costs you nothing to advance the ignition and see if that doesn't improve the idle, right? That will at least tell you something. :-)

The first thing I'd do is check your fuel pressure with a gauge like this. If your fuel pressure is at or about 60 PSI then visually inspect the barrels of the throttle body while having someone key on the Sniper. You should get a light spray evenly distributed in all four barrels. With everything else being right and since you can make it start by adding fuel it seems like you must have some sort of fuel pressure issue. I have certainly seen this before on other fuel injected vehicles when hot. It might be necessary to insulate or re-route your fuel lines if this can't be solved any other way.

I certainly appreciate your frustration (as well as your wife's!) Intermittent stalling usually points to radio frequency or electro-magnetic intereference (RFI/EMI). I have an entirely separate article on Solving RF Intereference Issues. I would suggest you take a look at that if you haven't already.

Not to bandstand here but this is the point when where you bought your system is so important. If you can send a data log to the vendor from who you bought your Sniper EFI System they should be willing and able to take a look and recognize RFI and then give you some ideas on solving it. We do that but most places don't. They tell you to ask call Holley. Holley will take a look and tell you you have RFI and wish you good luck in finding it. But, whether your vendor provides you with tech support or sends you to Holley, I'd start by getting them a data log and asking for some insight.

I have not heard of this. I presume your idle speed table doesn't increase at 200 degrees? If you haven't confirmed that they it is worth checking. It would be possible to set up a 1D or 2D table and do something like this, so if you've gotten into these advanced setups then that would be another thing to check.

If neither of these work then I'd recommend that you do a data log of the engine idling as the temperature is reaching and then exceeding 200 degrees. Then you can take a close look at the IAC and see if it is opening. If it is then something is commanding the ECU to open the IAC. If not then you have some other issue that is behind this increased idle. In that case, and if you have an EGR valve, I might be suspicious of something going on there.

I'm going to jump out on a limb here and say you either don't have adequate fuel flow or pressure. Have you confirmed your fuel pressure at idle is 60 PSI? Have you checked your fuel filter and made sure it's not plugged?

If both of these are okay you're going to have to find a way to monitor your fuel pressure while under load. The Super Sniper will allow you to monifor fuel pressure if you add an electronic sender but this is not an option with the standard Sniper. Holly offers a very nice Analog-Style Fuel Pressure Gauge that is another option.

Ok, so there are a couple peculiar things going on here. If the engine idles at 750 RPM with the throttle plates all the way closed and the IAC at zero then there is some sort of an issue. A couple of possibilities that come to mind in order of likelihood:

• You have a vacuum leak somewhere.
• The IAC is hanging open and not really at 0. See these IAC Test Procedures.
• The throttle plates are misaligned. Honestly, I've never seen this happen but if the butterflies were misaligned on the shafts it could allow too much air to enter. When the idle speed screw is turned all the way out there should be just enough room between the bore and the blade to catch your fingernail.

What you are experiencing is rather common. The IAC going to 30 is normal. That is the IAC hold position. It is temperature dependent but 30 is commonly where you find it. The hold position is part of the response that keeps the car from dying when you come off the throttle. You can adjust this number up or down but there is really no need to change it unless the car is stalling.

The sucking sound is just what happens when the Sniper EFI System is paired with certain intake manifolds. It is easily solved by installing a four-hole gasket or four-hole spacer (depending on your hood clearance issues.) These will fix the noise but if the performance is suffering then likely you won't see any difference since it is not likely to be related to this sound.

If the solutions suggested above are not working then you need to review my article on IAC Testing Procedures. Once you confirm the operation of your IAC then it's time to read my article on Solving RFI Problems. Your issues are likely related to one of these two things.

This question is really outside both the scope of what we try to discuss in the comments section as well as the overall subject of this article. However, it is a good question so I thought I'd throw a few bits of info out there that I think might help.

First, I believe that you may have a basic misunderstanding of what is being referred to sort of generically as AFR. In the context of the Sniper the AFR that is being displayed is the AFR of ethanol-free gasoline based on the lambda that is being read by the AFR. When the lambda is 1.0, the displayed AFR is 14.7;1 REGARDLESS OF THE FUEL. So if you are trying to achieve a stoichiometric mixture in ethanol (which is achieved at an AFR of 9.0:1) then you should continue to target 14.7:1 since that is what will be displayed. Don't try to correct for the fuel.

Second, Holley just released over the weekend a video on how to implement a flex fuel sensor on their HP and Dominator ECU's. While this video is not meant for the Sniper EFI user it does provide a great overview of how your ethanol tuning adjustments must be made not only to the base fuel map but to the other configuration settings. Give it a watch: https://youtu.be/7SO7-tZn6iw

Ok, so I'm stumped! Given the circumstances I would say that it is either the IAC motor itself or RFI but you seem to have ruled both of those out. If I were there in person I would test the function of the IAC (see this article.) If that tested out okay then I can really guess that there might be some sort of intermittent, temporary RFI. I've not heard of any others with this exact issue so I don't think it is a common problem.

There is no real mystery here. Somehow air is entering the engine that was not entering the engine when you originally set the idle speed screw. Your task will be to find that. Since it is unlikely that anything else changed it is most likely the IAC is problematic or the butterflies are not shut all the way. The next time it happens is the perfect opportunity to find the problem. With the engine still idling high park, set the brake, open the hood, and remove the air cleaner.

There is a chance that the IAC is open but displaying 0% so start by putting your finger over the IAC opening. If no air is passing (and the idle doesn't drop) then your IAC is working. Next, reach down into the secondaries and push the butterflies closed. If they are closed, check the primaries. Don't be surprised if one or the other is slightly open. If this is the case then some adjustment of the linkage or the butterfly plates themselves is necessary. Another suggestion is to add an extra turn to the spring built into the linkage to increase the closing force on the throttle shaft.

Well you were right air was entering from another source. Cracked casing from a side cover screw being installed crossed threaded. Holley have given a new unit. Seems to behave more better now. But I still get the iac at 0 and the rpm at 1200. Going back to what you said. If the screen shows iac at 0 and you block the hole to find it open what does that mean?

If you see that the ECU is commanding the IAC to 0 but there is air entering the IAC port then it's time to refer to my article on IAC Testing Procedures

Whenever we see the AFR go to "Heating" that is an indication that the ECU has been reset. It could be a problem with the power/ground for the Sniper but much more commonly this is a result of too much RFI. Fortunately, I have an article that goes into this in some detail. I recommend you have a look:https://www.efisystempro.com/efi-pro-hangout/holley-sniper-efi-instruction/solving-sniper-rfi-problems

I would start by removing the progressive linkage. The progressive link can be a great solution on standard (non-Stealth) throttle bodies but I would install this LAST after everything else is working perfectly. If it creates an issue (not normally the case) then you'll know. It's going to be really difficult to nail down the problem with the several simultaneous changes that you've made. Take it a step at a time.

If the TPS reading on your Sniper EFI System does not reset to zero that is a problem that needs to be addressed. Contact whomever sold you your system or Holley directly. There is no sense proceeding until your TPS is at zero at key-on.

Let me be perfectly clear: If your engine will not drop below 1350 RPM with the idle speed screw turned all the way out then you have an air leak. That is the first thing you must find. It could be that you've left a vacuum port unplugged, it could be that the throttle plates are misaligned (unlikely), it could be that your IAC is not closing properly. But you've got to find where air is getting into your engine.

The reason it's going up as high as 2400 RPM is because once you press the throttle beyond 1% the IAC opens to the park position. That, on top of your air leak, is allowing the engine to idle at 2400 RPM. But once you come off the throttle there is a minimum RPM that the ECU wants to see before it releases the IAC from the park position and that is normally 1000 RPM over the target idle. Since your target is probably more like 700, and since 2400 is way over 1700 RPM, it's going to leave the IAC in the park position.

Buckle down and find how air is getting into your engine. These problems will go away when you do that.

That initial rev is going to be determined by your IAC Park Position. Reducing that a bit will help. I go into much more detail about that in this article on startup tuning.

The first place my eyes go when there is any issue with the idle is to the TPS value. This will tell us if the ECU thinks that it is in control of setting the idle or if it thinks that you are driving the engine speed with the pedal. If the TPS is 1% or below then the ECU is in control--2% or greater and the ECU thinks you've got it under control.

If you look down and your TPS is 2% then either your throttle is stuck slightly open (which itself will cause the idle-up) or RFI riding on the TPS signal has caused the ECU to see the throttle as open and, as a result, open the IAC to the hold position. This value is itself enough to raise the idle a bit. Once you know that then you can work on those problems.

If the TPS is 1% or below then the air is coming from somewhere else. Sometimes an engine can produce enough vacuum to pull the secondaries open slightly. If you suspect this then try to find a situation where this occurs where you can safely check the secondary throttle shaft and see if i's slightly open. Adding a wrap to the return spring on the shaft is one alternative to solving this.

Your comment doesn't imply any sort of problem that would make me give up on idle timing control. You just need to go back through the IAC adjustment procedure now that idle timing control is enabled. Even then, recognize that over time the IAC will need to be readjusted to compensate for minor changes that will cause it to drift. I was looking at a data log from my truck earlier this week and noted that at idle my IAC was zero. No big deal, just time to re-adjust!

Both answers you've received greatly oversimplify the truth in favor of the answerer. The whole topic of using the Sniper TPS for transmission control is one deserving of it's own article but I'll try to summarize a bit here.

I have driven a stand-alone transmission controller for the 4L60E in my (then) Sniper-equipped '95 GMC pickup using the Sniper TPS with complete success. So, clearly, the "No" answer is wrong. And the rather cavalier "Absolutely!" I received from the controller manufacturer greatly understates (at best) the repeated failures of others I know personally who have tried and failed.

Key, I believe, in this success is solid connections, resistance-free signal and ground paths, and solid RFI rejection. I used the Casper's Electronics 108103 splitter and carefully soldered my connections. I cut and heat-shrink wrapped the 5V wire and then ran both the signal and ground wires all the way back to the transmission controller. I emphasize "and" because the transmission controller manufacturer I used had the TPS ground terminated within the harness to the unit's main ground, which I find to be an unthinkable choice. They also recommended that their ground be spliced into the Sniper ground as close to the Sniper as possible. Um, no. Both Sniper and trans controller grounds were direct to the battery ground, as they should be.

To finish, I rather tightly twisted the TPS signal and ground wires all the way from the controller to the Sniper TPS and very carefully routed them away from sources of RFI. I never had a problem with this. But I can tell you that for most people who try this it introduces so much RFI onto the Sniper that it never works right.

If you feel you have no other choice but to run a Sniper and stand-alone controller then you can give this a try. But now that Terminator X is available, I highly recommend going that route. In addition to avoiding this particular problem, the total solution is much better. I have an entire article on choosing between Sniper and Terminator X throttle body solutions and while Sniper is still a sound choice for some applications, Terminator X (with transmission control) is hands-down the way to go for those who need that.

So glad this was helpful. Great work, expert!