Iac?
Thread Starter
Intermediate
Joined: Feb 2012
Posts: 35
Likes: 0
From: CT
Iac?
long story,I bought this 88 vette about a year ago(been lurking here learning and reading for longer)anyway the car has never ran right.
idle quality is poor surges,stalls,idles high between shifts.I originally
believed the car to have a vacuum leak.I have capped every vacuum fitting with no change.I replaced the IAC valve,reset minimum idle,
adjusted tps no change. Today I jumped the diagnostic port waited 30
seconds and unplugged the IAC started the car and adjusted the idle to about 1K left the IAC unplugged took the car for a ride and ran and drove better than ever! no check engine light.car has a 383 edelbrock heads,longtube headers,edelbrock intake and runners.no idea if the computers ever been tuned.could a out of wack tune cause the computer to do wierd things to the iac valve?
idle quality is poor surges,stalls,idles high between shifts.I originally
believed the car to have a vacuum leak.I have capped every vacuum fitting with no change.I replaced the IAC valve,reset minimum idle,
adjusted tps no change. Today I jumped the diagnostic port waited 30
seconds and unplugged the IAC started the car and adjusted the idle to about 1K left the IAC unplugged took the car for a ride and ran and drove better than ever! no check engine light.car has a 383 edelbrock heads,longtube headers,edelbrock intake and runners.no idea if the computers ever been tuned.could a out of wack tune cause the computer to do wierd things to the iac valve?
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
depending on the spec of the engine ( esp the cam ) a stock tune more than likely won't cut it
Example ,
if a bigger cam requires the engine to idle at 800RPM and the stock tune calls for 450 , then the ECM will be constantly trying (unsuccessfully ) through the IAC to pull the idle down to a level the engine won't run at
There is no feedback on the IAC so you will never get a SES light regardless of what the IAC is doing or if it is even connected
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
It sounds like you could benefit from attaching a diagnostic tool to the ALDL and run the car to see what's going on with the ECM.
Also, you could check engine vacuum at idle to verify there are no vac leaks.
Also, you could check engine vacuum at idle to verify there are no vac leaks.
Last edited by 65Z01; May 2, 2013 at 01:36 AM.
