To clarify, the IAC at 23 was after a test drive and the car fully warmed up. The next morning on a cold start, the IAC is at 160. It seems I can get the values (IAC, TPS, idle) where it should be warmed up but it will not high idle when it is cold.

I'll enlarge the hole again and see what happens.

Fred - I have not tried the stock TB yet. Bryan from PCMforLess also suggested drilling it so I went ahead and did that.

 

You want the BLM's (long term fuel trims) to be close (not split), not the INT's (short term fuel trims). If the BLM's are stable, the INT's will average 128 over an extended period of tims.

 

When cold, the IAC counts go to 160, but the engine does not idle at higher RPM, correct?

Either there is something blocking the idle air flow, or the IAC pintle is not actually moving.

 

OP

when you swaped the IAC over from the stock TB....did you compress the printle by chance?? (you don't want to push in printle)

 

I swapped the IAC valve over from the stock TB a few years ago and it has not idled well since then. I was aware of the potential to damage it if the pintle is pressed and I don't believe I did but can't say for sure.

Bryan (from PCMforLess) looked at a data log I made last night of 2 hard pulls and noticed my TPS is only going to 3.5V WOT. Also, at closed position, the TPS is 0.43. I have the GM Service Manuals and know this is within the correct range but Bryan and many believe others I should adjust it to the center value 0.67V. I will do that next.

I am going to replace both IAC and TPS with new ACDelco parts to rule these out since they are both very old and neither is the original (may be Airtex or Standard).

Will update after new parts installed.

 

Fred, that is correct. See previous post where I mention that Bryan noticed incorrect WOT voltage from TPS. I will replace both IAC and TPS to eliminate these from the equation.

 

Does the scan show that the PCM is interpreting the 3.5V signal as 100% TPP?

 

agree it is best to get TPS closer to spec before any further "drill" is done.

Your IAC may be bad and possibly just failed or was damaged back when you swapped it from the 48

Your TPS does want to be .67vdc blades closed and 4.5 vdc full open. If you have a volt meter or scan tool watch vdc increase as you SLOWLY open blades. VDC should increase steady and not have any dead spots or spike when you do this.

I suspect the aftermarket TB blades are not set right and the TPS readings are low as a result. Once you get TPS back in the mid time zone scan IAC counts again. You then may need to drill TB more if they are still high at idle

....or you could put the 48 back on but if this is a A4 car Brian would want to adjust the PCM back for that

an alternate "trick" to get TPS right is slot the holes and "turn" it back to adjust VDC....I am not onboard with that method but many have done it.

 

Some good news finally! I fixed the idle problem.

I bought a new IAC servo and a TPS (both ACDelco) to rule these out. When I removed the IAC, I noticed the lower screw was loose. I also remember that when I re-installed it a month ago or so, I noticed the O-ring was loose so I replaced it with a new one. Not sure if it was sealing properly. I also performed the IAC reset procedure with the new one. The car is now idling like a champ right at 800 even with a very cold start.

Before I replaced it, the IAC count was very sensitive to adjustment of the throttle plate stop screw. It would shoot to 0 or 160 with a very small adjustment of the stop screw and it would not hold a steady value very well. Now the adjustment is very stable.

I suspect I may have had an air leak around the IAC but it could have been the valve itself or the reset that fixed it.

I also found the TPS was not going all the way to 0.45V at full throttle. It was maxing out at about 3.5V even though the reference voltage was 5.0V and the ground was good. I determined the floor mat was under the pedal preventing full travel. DOH!

Now I am idling at 800rpm with IAC count 30 and the TPS voltage is 0.60. I can't get it to 0.67 without slotting the TPS but this is close enough.

So the idle problem is solved but I think I have either a bad O2 sensor or a split long term BLM problem that will require enlarging the 1/8" hole I drilled in the TB. The right side is running rich (153) and the left side is a little lean (126) at idle. The O2 trace is showing the right O2 sensor is not consistently sweeping from 0.1 to 0.9. It is more like 0.1 to 0.7 and sometimes it does not oscillate fully. It may have been damaged by the oil fouling on the right side which caused me to rebuild the engine. The sensor looked OK on the outside when I re-installed.

All gaskets and seals are new and tight so I know I don't have any intake or exhaust leaks therefore I suspect the O2 sensor. I am going to swap the O2 sensors to see if the problem follows the suspect O2 sensor. The injector pulse width is much narrower on the right side too which is consistent with a rich right side and the PCM is trying to correct.

Will let you know what I find. Thanks for the help so far guys. I did not suspect the IAC itself was bad.

 

your IAC counts and TPS VDC are good. Don't drill the hole any bigger.

Your split BLM's are other issues. Swap the 02 to see if the problem migrates to the other side.

 

Should be able to get that done tonight. Will let you know what happens.