idle speed
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
You don't - idle is controlled by the ECM which pulses the Idle Air Control Motor in and out to control the flow of air through the throttle body. Easiest to test with a scanner which will show you the programmed or targeted ECM idle speed, actual idle and the number of steps or counts the IAC is taking to maintain the targeted speed. My guess would be that the IAC on your Vette has jammed and is letting in too much air. You can try to reset it by grounding the diagnostic link which should fully extend the pintle. You might even be able to hear it run. Afterwards, slightly depress the accelerator and start it. Let it run for 10 seconds. Shutoff and restart. Idle should be normal. If not, and absent a scanner, you might try a new IAC, but clean the throttle body too if you do replace it.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Indeed a vacuum leak can cause high or erratic idle. I had this happen on the IROC due to a leaking EGR valve diaphram. Aslo check other vacuum hoses.
Also, clean the TB and the IAC & it's bore (under the TB); then reset base idle and the TPS voltages.
Also, clean the TB and the IAC & it's bore (under the TB); then reset base idle and the TPS voltages.
Heel & Toe
Joined: Mar 2004
Posts: 21
Likes: 0
From: Easthampton MA
I had a similar problem with my '85. The EGR valve gasket was the problem. I ended up removing the intake plenum and that gave good access to the EGR valve. The holdown bolts were loose. 1 of them is a real bear to get at; My guess is if that's your problem, it's that bolt... Good Luck.
