I have this intermittent idle problem on my car now (85 vette). Most of the time, it cranks and runs fine, but sometimes it will not run without my foot on the gas. I had the IAC cleaned and throttle body, but it hasn't completely went away. For a temporary fix, I turned the idle screw up so it will idle when the IAC doesn't seem to work, which has become more often. When it does decide to work though, the car idles really high, so I have to turn the idle screw back down, or spin the tires shifting into gear and idling at 50mph!

So is the IAC just going out? I already have a new one, and install seems simple, but could there be something else wrong? Car runs perfect otherwise!

 

replace it,later jimmy

 

replace the iac and do the specific tuning instructions and re-set your TPS voltage. the tps sensor has to read .54volts. when you messed with the idle screw you messed with the voltage reading on the tps

go to tech articles on this site and it will tell you what to do.

also wouldnt be a bad idea to check your spark plugs check MAF sensor and replace your fuel filter which is like 15bucks

 

Look for vacuum leaks at the Throttle body and check for cracked plastic lines. High idle speed means more air. Could be air leak or iac. What are the iac counts doing. more counts, more air, less counts less.