Okay, I have this lingering problem I can't seem to diagnose properly.

The symptom is the idle wants to creep up to about 1300-1500. I have replaced both the Idle Air Control valve motor and the Throttle Position Sensor (2X). and the problem keeps returning. I have searched out any leak, but haven't seen or found anything. When the throttle body was off, I cleaned it thoroughly and replaced the manifold gasket.

And here's the extra bonus information to really screw with you:
AutoTap will identify the TPS sensor moving around (~5-10%) when the throttle is closed (yes, it really is closed), and then the IAC count will move from ~60 to 130, then the idle climbs right afterwards. Throttle blips have no effect. The Throttle body is an AS&M and is not suffering from a sticky throttle plate problem (like my old BBK). If I turn the key off and back on, the TPS will go back to 0.0%. Also, even though the TPS may be showing 5%, the TPS voltage remains low at 0.5V ().

Should I remove my blower belt and see if that has any effect? My MAF is now mounted on my 90* elbow (blow-thru). This is a new problem that surfaced recently. I did have a TPS error code and replaced my TPS (1st one) and that fixed that problem, but now my idle is creeping and driving me nuts.

 

i am having the same problem as you. my throttle body is causing the problem. on the linkage side where the shaft goes through the housing it has a little play in it and i am not sure if air is coming through the housing or just slipping by the butterflies. but when the car is ideling i can move the linkage just barely side to side(not rotating it) where it has some slack in it and it will idle down. double check your t/b and make sure everything is good and tight on it.

 

Okay, I spent a few hours fiddling on this one yesterday and here's the breakdown so far:

1)I removed the blower belt to isolate the problem from the blower. The problem did not go away. (Not a supercharger-induced problem). I had a suspicion that the SC was pushing air past the butterflies or through the IAC more than desired.
2) I began inspecting the wiring harness supporting the IAC and the TPS. Both looked twisted and mashed near their connectors. I removed the TPS connector and snipped it off (3") and metered it for connectivity. During my ohm metering, I thought one of the connectors was flaky, wiggled it about, but determined that it was not the problem. I added about 3 inches of extra wire and soldered all connectors back on. The IAC looked a lot better. I also straightened out any crimps that may have been contributory. (Note: these wires are small gauge and multi-strand).
3) After cruising around (without the blower belt...now that's a weird sensation) the problem seemed to go away completely. I had Autotap running and the TPS voltage was 0.5V @ 0.0% TPS. I must've put about 40 miles on it and no problem. (this was an illusion)
4) I put the belt back on and within about 2 miles, the problem came back...AHHHH, but now the Autotap readings are getting weird....Now while driving around//
I noticed that my TPS voltages would drop to 0.2V @ 0.0 TPS sometimes. When that occurred, I noticed that the TPSV would occassionally fluctuate between 0.2V and 0.5V, except when the voltage went back to 0.5V, the TPS sensor reading was now about 5% open (throttle actually closed). What I was seeing was a fluctuating voltage feeding my TPS sensor.

So I thought for while about where does the TPS sensor get its 0.5 volts. If it was native power, it would be 12-14V, and there isn't any secondary power source....except the PCM.

Lucky me. (LT1 Edit has taught me one thing in absolute terms. Always have a spare PCM because you will eventually blow the original and then you're dead-in-the-water.)

Swapped the PCM, reloaded the best LT4/PCM4LESS program, changed a few variables to fit my particular situation.

So now....(fingers crossed, eyes crossed), the car is running great. The TPS voltage is steady at 0.5V and idles like a kitten at 800 RPM. I suspect that there may have been a wiring harness problem that was creating some resistance between the PCM and TPS, but with the swapout, I may have reset its connections. I hope this is the end of this bug. Intermittent opens are one of the worst bugs to troubleshoot, especially when they only partially open and create resistance opens.

 

I had the same problem ... cleaned the IAC ... relief for a few weeks then the idle would wander again. Also, I never liked the ECU holding the idle high when decelerating or driving in snow. My ultimate solution was to plug the air supply hole for the IAC that's in the front of the throttle body.
Problem solved! In very cold weather the car starts at about 600 rpm but is up to the normal 800-850 rpm (M6) within a few minutes. No other effects. No problem with emission testing either. It actually had better numbers after the plug! (if you accept the state equipment as accurate!) You might have to adjust the throttle plate stop. I played with it but only about 1/8 of a turn was needed.

 

Put another 50 miles on it...no problem as yet...