Idle Question
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Instructor
Joined: Jun 2004
Posts: 121
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From: Snatch BC
Idle Question
I just did a full tune up on my 86 Vette this weekend car runs excellent. I however have an on going problem that I cant figure out. For some reason every once in a while my car will go down to 600 RPM down from the 800 RPM it usually idles at. Any ideas as to what this could be ???
Pro
Joined: Mar 1999
Posts: 678
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From: Oslo, Norway
Hi.
I have an 85 but I think there is not that much difference in the idle speed. I have another ECM. The idle should be around 600 rpm. Did you do a minimum air idle speed adjustmeny to assure that the min air adjust gives about 450 rpm when the AIC valve is closed. Look in the manual to see the accurate adjustment. The idle is set in the prom in the ECMand acnnot be adjusted. If you have cycling idle it might be carbon deposits in the throttlebody and the AIC valve. Clean it if you have anything there. Check the vacuum lines toavoid false air as that also make the idle cycle a bit.
Just some hints
Jan-Erik
I have an 85 but I think there is not that much difference in the idle speed. I have another ECM. The idle should be around 600 rpm. Did you do a minimum air idle speed adjustmeny to assure that the min air adjust gives about 450 rpm when the AIC valve is closed. Look in the manual to see the accurate adjustment. The idle is set in the prom in the ECMand acnnot be adjusted. If you have cycling idle it might be carbon deposits in the throttlebody and the AIC valve. Clean it if you have anything there. Check the vacuum lines toavoid false air as that also make the idle cycle a bit.
Just some hints
Jan-Erik
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
[QUOTE=Black_Vette]I just did a full tune up on my 86 Vette this weekend car runs excellent. I however have an on going problem that I cant figure out. For some reason every once in a while my car will go down to 600 RPM down from the 800 RPM it usually idles at. Any ideas as to what this could be ???[/QUOTE
Many times this is caused by a sticking IAC (Idle Air Control). Over time, a build up of carbon on the pintel will cause the IAC to respond sluggishly resulting in a unstable idle .
This carbon build up also effects the closing of the throttle body butterflies. Carbon builds up on the backside of the butterflies and needs to be periodically cleaned off.
You can try removing the IAC and cleaning the pintel with an old tooth brush and some spray carb/injector cleaner. The best way to clean the butterflies is to completely remove the throttle body from the plenum. Doing it that way will allow you to clean both the IAC and the TB at the same time.
Hope this helps.
Jake
Many times this is caused by a sticking IAC (Idle Air Control). Over time, a build up of carbon on the pintel will cause the IAC to respond sluggishly resulting in a unstable idle .
This carbon build up also effects the closing of the throttle body butterflies. Carbon builds up on the backside of the butterflies and needs to be periodically cleaned off.
You can try removing the IAC and cleaning the pintel with an old tooth brush and some spray carb/injector cleaner. The best way to clean the butterflies is to completely remove the throttle body from the plenum. Doing it that way will allow you to clean both the IAC and the TB at the same time.
Hope this helps.
Jake
