Alright all, I have a Brain teaser for you. I have a 1996 Chevrolet Tahoe with the Vortec 5.7l, it is idling between 1750 to 2000 RPM all the time. I have already inspected, Cleaned and replaced the upper and lower intake gaskets, Octopus O-Ring, PCV, throttles body gasket, brake booster O-Ring, EGR gasket/ Verified the EGR operation,cleaned and de-carboned everything and replaced the IAC, The MAP, + tested the IAC circuit with a Fluke DVOM and with my Snap On scan tool, attempted to adjust the idle by cycling the ignition switch. Sprayed the entire Intake down with water and carb cleaner with no change. The only thing that changes the idle is if I physically plug the iac port with my fingers. I have 10.6 volts between the A and C pins on the IAC and 8.4 volts between the B and D pins of the IAC circuit. The ECM connector is pristine and I have inspected the engine wiring harness. The hi idle started after I loaned the vehicle to a close friend who more or less screwed me by beating the crap out of it, it ran without a hiccup before the loaner incident. Is it the computer? I am a Master certified mechanic by ASE and the state and have checked about everything but I specialize more in Fords and Chryslers, so any help would be appreciated. Thanks.

 

Maybe you got a bad IAC out of the box. Just a shot in the dark.....

 

So I Pulled the iac out and physically pulled the plunger out and reinstalled it the idle came down to about 700 rpm but gradually worked its way back up to 2500 rpm. The computer is pumping the idle up and I don't have any references to check against my readings as I stated before i am primarily a Ford/Chrysler Mechanic and have no Professional Chevy Mechanics in my mechanics circle.

 

Is there free movement of the throttle cable and throttle plate?
try removing the throttle cable from the body and see if its the cause