IAC adjustments
Thread Starter
Safety Car
Joined: Oct 1999
Posts: 4,679
Likes: 2
From: Honolulu HI
IAC adjustments
While trying to reset the idle, which I am familiar with the procedure, I cannot get the engine to hold a steady idle speed with the IAC disconnected. I can't set the RPM at 400-450 because it keeps surging back and forth from 400 - 800 RPMs. Any suggestions on why? Any info. much appreciated.
Aloha,
Larry
Aloha,
Larry
Le Mans Master
Joined: Jul 2001
Posts: 6,252
Likes: 2
From: Silicon Valley Kalifornia
Re: IAC adjustments (Larry Mackey)
Mine is right by the brake booster...between the booster and engine; by the firewall. It's a free hanging connector. Just pull apart after releasing the lock tab. :flag
Burning Brakes
Joined: May 1999
Posts: 760
Likes: 1
From: Greenwich, CT
Re: IAC adjustments (Larry Mackey)
Larry:
I was doing some tuning on my '91 over the summer, and had a similar situation. I found that the EGR was sticking part-way open - this acts like a vacuum leak at idle, and was a bear to diagnose correctly using Diacom. (If you want to try a diagnosis test, make an EGR block-off plate to sit in the EGR connection just above the right side header - I used a scrap of aluminum bar stock.) You might also check for excessive exhaust back pressure - there is a test described in the GM manual. A bad PCV valve could also be a vacuum leak at idle.
In the end I replaced the EGR valve & solenoid, plus the O2 sensor and it cleared things up on mine. FWIW, I also found that one injector was leaking, and put in a new set of those as well - all these parts were original equipment on mine, and I guess 10 years was a pretty good run but they needed to be renewed.
If your EGR system has not been checked recently you might consider it as a possibility, or the other items mentioned above. HTH
drj
[Modified by DOCTOR J, 4:03 PM 10/1/2001]
I was doing some tuning on my '91 over the summer, and had a similar situation. I found that the EGR was sticking part-way open - this acts like a vacuum leak at idle, and was a bear to diagnose correctly using Diacom. (If you want to try a diagnosis test, make an EGR block-off plate to sit in the EGR connection just above the right side header - I used a scrap of aluminum bar stock.) You might also check for excessive exhaust back pressure - there is a test described in the GM manual. A bad PCV valve could also be a vacuum leak at idle.
In the end I replaced the EGR valve & solenoid, plus the O2 sensor and it cleared things up on mine. FWIW, I also found that one injector was leaking, and put in a new set of those as well - all these parts were original equipment on mine, and I guess 10 years was a pretty good run but they needed to be renewed.
If your EGR system has not been checked recently you might consider it as a possibility, or the other items mentioned above. HTH
drj
[Modified by DOCTOR J, 4:03 PM 10/1/2001]
Burning Brakes
Joined: May 1999
Posts: 760
Likes: 1
From: Greenwich, CT
Re: IAC adjustments (Larry Mackey)
Larry-
I'm up to about 45,000 mi. The parts replaced were due to age, I think, not mileage. We just don't get that weather here like you do - it has to sit in the garage for half the year.
here's what it looks like currently:
http://www.corvetteforum.net/c4/doct...1-SRRt15Sm.jpg
dave
ps - getting to the EGR is a real joy
[Modified by DOCTOR J, 4:27 PM 10/1/2001]
I'm up to about 45,000 mi. The parts replaced were due to age, I think, not mileage. We just don't get that weather here like you do - it has to sit in the garage for half the year.
here's what it looks like currently:
http://www.corvetteforum.net/c4/doct...1-SRRt15Sm.jpg
dave
ps - getting to the EGR is a real joy
[Modified by DOCTOR J, 4:27 PM 10/1/2001]
