Recently, I took out the throttle body in my 87 Coupe to clean it up. I used 2 spray cans of carburetor cleaner, lots of rags and a toothbrush. The Idle Air Control valve was removed and cleaned. Everything was sparkling clean when reinstalled in the car. I followed the instructions found at:
http://www.geocities.com/jgkov/IACService.html

All electric connectors were checked and the TPS was adjusted to 0.54Vdc following the instructions in:
http://www.geocities.com/jgkov/TPSService.html

When cold, the car starts immediately, revs to about 800 rpms for a few seconds and drops to 500-600 rpms, which is fine. After warm-up and driving for a few minutes, when I stop at a traffic light or whatever, I shift into neutral and find that the idle is 1,200-1,400 rpms, which is too high. Then I "blip" the accelerator pedal and the rpms drop to 500-600. I even sprayed a bit of WD-40 in the throttle linkage to see if the problem was due to a sticking linkage but the problem persists.

I tried to pull codes using a jumper from terminals A & B in the ALDL and there are no codes. This method was found at:
http://www.c4vettes.com/ecm.htm

The MAF sensor and both relays were installed 2 years ago. The engine has no internal mods, only a KN filter with cut lid, throttle body airfoil, by passed coolant in the TB, Bosch 4+ spark plugs.

This high idle makes my engine run hotter and everytime I get stuck in traffic, I have to shift into neutral to "blip" the pedal and bring the revs down, which is a PITA.

Any suggestions? :mad

 

I have a similar problem but if i blip the peddle it doesn't return to proper idle. Mine after sitting for a sometime slowly makes it's way to normal idle. I am blameing my IAC for it. Your acts like a sticky throttle cable or throttle valves. Disconnect the cable at th TB and see if you can determine if either of them is the culprit.
:cheers:

 

Replace the IAC $60.00 at GM.

 

I need to replace my AIC as well. I have an erratic idle issue as well