maybe you have to make some fueling adjustment so the car will want more air. it was a lot to read but from what i saw you had + trims. if u add more fuel, u get them negative, the car will get more fuel and maybe need more air for the IAC to want to open up more. i have a post going about how i adjusted my idle and its worked very well. as i was making these changes i saw my idle iac count get higher and higher. i started at 40 iac steps and when i was done they were at 55 or so. i opened the tb blade some more and decreased idle airflow and now my iac is at about 30-40. something worth looking at. if you want to pm me feel free to and ill try to help ou out somemore. maybe you could give me a quick rundown on whats going on now and whats been done.

the only thing that gets me is that it was like this stock, so i would think like what the others are and say its a leak somewhere, but if you have had no luck so far then you can try somewhere else. pm me if u want me to explain this more and if i was confusing lol

 

Adjust the throttle blade set screw so that it reads 0.53v at idle then retune your idle trims. You don't need to alter any IAC calibrations in the VCM. If you have low IAC counts, its because of a modification, more likely the TB letting too much air around the blade.

When reducing airlfow, you also may need to adjust the base idle spark. Always check for happy O2 sensors.

If you still have 0 IAC counts, then adjust the blade back further up till around 0.47v. You have to be careful around this limit as the blade can expand when hot and cause sticking, or you could adjust too far and the blade falls over backwards.

Its somewhat trial and error.

Regarding the floating at decel. thats because the IAC is remaining open. Try adjustuing the throttle follower to increase the rate of decay of airflow. If no luck, then reduve the throttle cracker values 0-1200RPM and 0-6KPH.

 

In response to the replies above, I don’t think any of that applies to my situation. This car should not require any tuning or TB blade adjustments to idle properly, it’s stock other than a lid and catback.

In addition, the IAC counts do not always stay at 0. Most of the time they are somewhere in the 8-16 range at warm idle depending on run time, exact coolant temp, P/N vs in gear, etc. They only time a 0 IAC position is observed is when the idle hang condition is occurring, and the idle issue seems to be a totally random condition.

I have checked and re-checked everywhere for a vac leak and I can’t seem to find one. It does seem like the most likely culprit but it just doesn’t seem to be there. I’ve thoroughly checked all around the intake, the TB, the PCV system, air bellow, vac lines to the intake, etc., and found nothing. The EVAP and EGR systems *seem* to be working properly, though I’m only basing that on the fact that I’m not getting any DTCs for either. I suppose if there was a slight issue with the EGR valve it might allow a tiny leak that may be too small to set a DTC. I may try a different EGR valve just to see if it makes a difference....

Currently, my TPS is at 0.6v at idle. It’s a 100% stock TB. I am hesitant to adjust the TB set screw because that shouldn’t be necessary on a stock car, and 0.6v is within factory specs. Even if that helps the issue, I’m concerned that it may just be masking another problem. I am willing to try it, but why should it need that in the first place? Factory incorrect adjustment? Has that ever happened to anyone before?

What makes this whole issue so difficult to do anything about is its intermittence. Any hard changes that I make (like TB set screw) may negatively effect the idle under normal conditions as it seems to be fine most of the time to begin with.

I still haven’t been able to get anyone to confirm what their IAC counts were on a totally stock motor and TB with the stock A4 idle speed. I wonder how low my regular idle counts really are compared to other stock (a4) cars?

 

wonder if u may have a sensor going out. u have a maf on the car? and is it stock? maybe its giving faulty readings at idle causing this, thinks its getting air its not? just a guess, trying to go out on a limb to help you come up with anything lol

 

Thank you, believe me I certainly appreciate any ideas that anyone has to toss out there. I know this is a really long thread so I’ll recap on some things I you mentioned...

MAF is 100% stock. I’ve though about the MAF issue as well, so I cleaned the wires and the IAC counts were still low. Granted, the idle hang issue hasn’t happened since I cleaned the MAF but it’s always been very intermittent, only after extended drives, and clears up with an engine restart, so I really can’t say if that help it yet or not. LOL, guess it’s possible that the issue might already be fixed but I’m not usually that lucky. Besides, the MAF only has 12K miles on it, how dirty could it have been?

I’ve checked EVERYTHING to do with the TB blade sealing properly and the throttle cable working properly. Both are fine, throttle angle is usually 0.4% at idle (with a 0.6v TPS) which is the same as most other LS1s I’ve scanned.

Some parts have already been replaced in an effort to fix this. IAC motor, PCV valve, plugs, fuel filter, battery; to name a few. No change. O2 sensors seem to be working fine, neither is lazy and no codes present.

LTFTs do not seem to indicate any bank specific leak or issue. They are always within 2% of each other and many times exactly even. Usually they’re around ~ +5-6 at idle. Not the optimal readings granted, but not exactly indicative of an issue either.

No misfire activity detected, no DTCs of any kind, no other driveability issues.

The only thing in the data stream that points to an issue is the IAC counts....both the fact that they seem to be low all the time and that they are at 0 when the idle hangs (which is only occasionally). When the idle does hang, it’s only about ~100 rpm above desired speed, then it'll surge maybe ~50rpm or so in P/N. Not a huge issue I guess, but I’d just like to know if I can fix it.

I’m going to try another EGR valve. If that doesn’t fix it then I really don’t know what else to try. Guess I’ll just have to either wait for it to get worse and toss a code or if it never does then just accept it as normal for this car. No other option really....

 

I seam to have a similar problem with my 01 SS Vert. When I come to a stop, it idles at apx. 1k. After I sit for about 10 sec., it will return to normal idle. It just started doing this a few weeks ago. I have not made any engine mods.