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I have the Quadrajet Holley Sniper, its been running good, then it started floating around 2000rpm when I let off the throttle. not all the time, but most of the time. I noted the IAC reading was dead on twenty. sometimes a throttle blip will lower the rpm to idle, other times not.. Every time the rpm floats the IAC is twenty and the TPS is 0. I hate to start replacing stuff unless I have to. I was wondering if there is a test I can run on the IAC. maybe using a meter or something else. Also does someone make a better IAC then the one holley provided? Your thoughts and opinions will be appreciated. regards, Atlanta
If the IAC is sticking, common. Just replace it.
Quick test. Put your finger over the IAC air intake hole. If the issue is indeed the IAC, the idle should instantly drop. If the idle continues at 2K RPM. look elsewhere.
I have the Quadrajet Holley Sniper, its been running good, then it started floating around 2000rpm when I let off the throttle. not all the time, but most of the time. I noted the IAC reading was dead on twenty. sometimes a throttle blip will lower the rpm to idle, other times not.. Every time the rpm floats the IAC is twenty and the TPS is 0. I hate to start replacing stuff unless I have to. I was wondering if there is a test I can run on the IAC. maybe using a meter or something else. Also does someone make a better IAC then the one holley provided? Your thoughts and opinions will be appreciated. regards, Atlanta
If the handheld is reading 20 it is not sticking. It's a setting. Do you have a manual trans? If so the IAC hold pont and the decay need to be tuned. The default values for both were way too high for mine. I bet you will find the hold set for 20%.
It should hold, or park only when the TPS reads above zero. I agree the park position could be high, resulting in a push when removing your foot from the throttle. Like coming into a roundabout. But stopped still it should be able to drop the IAC to zero to find the set idle speed.
I believe we are mostly speaking about the same thing, but the point remains that if the handheld is showing a higher value for the position of the IAC, it is a software issue rather than a hardware one. The IAC is a stepper motor with no feedback. The count in the controller is differential and it knows nothing about the real position. If the position is unexpectedly high, this the software is commanding it to that position. It is either the target idle speed at that temperature or something is not re-enabling idle control.
In the Sniper the Park position is only for starts. The Hold is part of the Ramp. I would check the following:
Ensure the CTS is operating properly and not creating a high target (since you blipped the throttle and it came back down, this is not likely).
Check your target idle at the condition you are looking at (again, unlikely)
Check the IAC ramp down settings, particularly the Re-enable point. Setting this low could be an issue.
Check your throttle blades sticking in the bores. Common Holley throttle body EFI issue. I've had it with my Sniper 2 and thought it was the IAC. I found my blades sticking. Try to duplicate it in the driveway and when it happens press on the throttle linkage to help close the blades and I bet you idle will come down. It doesn't take much.
Checked the throttle blades and could not induce sticking hot or cold. So I took it for a test ride, about six miles with a little highway. It ran perfect, no issues. then as I entered my neighborhood let off the throttle and the iac went to 20 and the rpm was at 1500. Both held and would not come down until I put it in gear. which I think was from the load. just as before. The car is a manual, the sniper is only about two years old with not even a thousand miles on it. Blipping the throttle did nothing. At idle I put my finger over the iac port and the iac went from 2-14 each time I covered it. Here is a picture of my Iac control screen. any thoughts on if the iac is sticking. I note the hold time and decay seem long??? regards, Atlanta
It's not out of the possibility it's the IAC. When you put your finger over the IAC port did you also try to press on the throttle linkage to see if that's the issue. I'll post up my IAC decay settings when I can (at work right now). Also there is a bunch of good info in Keith's "Sniper for Dummies" sticky thread. Not specific on the Q-jet version but I suspect it's pretty much all the same.
Ok, I have been skimming through this thread, and without seeing a data log, everything is a guess. First off, your IAC hold position is 20 which I would consider normal. You could try 15% in order to promote less air into the engine and help you return to idle (I suspect that would be tuning around your real problem). Remember if your Sniper ECU is holding 20%, that means the software hasn't seen the conditions to ramp the IAC closed yet. As stated, that number is only what the ECU is telling the IAC to do. It is not feedback. What is your idle setpoint? If your RPM isn't returning to normal that is only because of one thing: too much air is still getting into the engine. That leaves you with: vacuum leak, throttle blade sticking, IAC failure. Throttle blades sticking after heat soaking is unfortunately a common problem.
As stated above, the IAC park position has nothing to do with running conditions, it only applies to startup. If your car is starting fine, don't touch that.
The next thing to look at is conditions to enter idle mode. If your engine is not getting below your RPM number (which I don't know what that is for your setup) PLUS the 1000 RPM you have as your "RPM above idle to start ramp" AND your TPS > 2 % then it won't ramp your IAC closed anyway.
Your "RPM above idle to re-enable idle control" only applies AFTER the rpm decreases to within (in your case) 100 RPM of your idle setpoint. So leave that parameter alone. It doesn't apply to your problem.
The IAC "hold time" and "decay time" only apply to the startup. Again, they have nothing to do with your problem. However, your ramp decay time in the non startup section is fine.
One thing you can do to test the IAC and return to idle: set your "RPM above idle to start ramp" from 1000 to 1500. That will cause your IAC to close at a higher RPM once you are off the throttle. For troubleshooting, you could even set it higher, like 1800. It's not going to hurt anything. If your IAC starts going closed earlier and you are still having return to idle problems it is more than likely the throttle blades. Then you'll have to ensure they are centered in the bores and go through that process. I am less familiar with the Q-jet version though. Does the Q-jet version operate as direct acting throttle plates or progressive out of the box? You can set up the Sniper either way, but I'm not sure about the Q-jet version. That would also make somewhat of a difference.
If you test drive it again, grab a data log, and save your running GCF. These can be analyzed and much of the pertinent information can quickly tell the story on what the Sniper is or is not doing.
I wasn't very concise in that last response. It was late and I was in a hurry to try and help. Let me try and clear up that post.
If your IAC is staying at your hold position of 20% the first thing that tells you is that you haven't met the rpm threshold for your IAC to begin ramping closed. Those conditions are: TPS < 2% AND your RPM is < (idle setpoint + "rpm above idle to start ramp"). For example: if your idle is 700 rpm and your "rpm above idle to start ramp" is 1000, then your rpm must be < 1700 AND TPS < 2% for the IAC to start closing. How fast it closes is set by the ramp decay time in that same "box" area.
When the above conditions are not met when the TPS < 2% it always means there is too much air still getting into the engine. That is caused by vacuum leaks (most common), sticking throttle plates (second most common), IAC failures (least common). IAC failures usually come with a slew of other starting and idling issues, so if the car is doing those other things correctly, I would lean away from the IAC failure as a last resort (although they are not generally hard to replace or deal with).
Keep in mind, that when the throttle blades are "closed" they are open a little bit. Usually only a .002" to .004". However, if the throttle blades are hanging up even a little more say an additional .002" that will be enough air flow to cause a high idle condition.
I looked up the direct vs progressive on the Q-jet Sniper. It appears they come progressive out of the box. I still don't know if it idles on all 4 barrels or not. Can anyone confirm this? The internet is inconsistent with the Q-jet information and my experience is only with square bore setups.
The idea of the throttle plate sticking with heat soak makes real sense to me. As stated before when I took it for a test ride two days ago it ran perfect until the end of the ride as I entered the neighborhood. then it floated. it was a 70 degree day. Today I did the Iac tune using the tape covering the iac port as described in sniper for dummies. It was dead perfect. Today the temp dropped thirty degrees here in Atlanta and the car ran perfect with no float. Everything seems to fit. My question is when it floats again and the iac says twenty should I expect the tps to also be high with a stuck throttle plate? And if the tps is 0 while the iac is twenty then what does that mean? Also if it is a sticking throttle plate when heat soaked then what do I do? Thanks for everyone's sage advice, It is very much appreciated... regards, Atlanta
Most likely its the secondary plates but I cannot confirm that as I run a Sniper 2 and it's a square bore with all the blades the same size. I'd have to look back at some of my data logs when I was battling this issue every time I drove it to see what the TPS was doing.
How to fix on the Sniper is to take it off the manifold and center the blades on the work bench. I made a "light box" to help. I put my Sniper on the box with a light in the box and you immediately see which blade is not centered. Loosen the screws (don't take them all the way out) and I used a magnet to move the blade around to center it. Make sure when loosening and tightening the screws you support the throttle rod so as to not bend it.
The last time I drove it the other day it was a little warm and I had the sticking problem. My theory is a Holley quality issue. It appears to me that these blades are just stamped steel with little to no machine work done on them. I would think the edge would be radiused but it seems to be flat and the consistency of the stamping is not good as some blades look fine and another is way off no matter how long I messed with it. Other than this my Sniper 2 is running pretty good. More tweaking to do but that's just part of modern fuel system tuning that never ends.
If the primaries stick than it is possible to see on the TPS. However, it usually happens on the secondary side due to either linkage binding, un-centered blades, or bore distortion. This is not detectable on the TPS since it typically comes from the primary throttle shaft.
To add to the sticking throttle plates theory, I know on my Sniper 1 (squarebore) the secondary return spring is not wound particularly tight. Adding another turn on that spring fixed an issue I was having with the secondary throttle plates sticking open.
To add to the sticking throttle plates theory, I know on my Sniper 1 (squarebore) the secondary return spring is not wound particularly tight. Adding another turn on that spring fixed an issue I was having with the secondary throttle plates sticking open.
Yes, before you try to address any "centering" try this first. When I get any new Sniper unit stealth or Sniper 1 or 2, this is one of the first things I do before even installing the throttle body. Good call.
To add to the sticking throttle plates theory, I know on my Sniper 1 (squarebore) the secondary return spring is not wound particularly tight. Adding another turn on that spring fixed an issue I was having with the secondary throttle plates sticking open.
I tried that but didn't like it because it was too stiff after that. I returned it to normal.
Sniper IAC Floats
