Cold Idle problem on 86 4+3
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Joined: Apr 2004
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From: Fairfax Virginia
Cold Idle problem on 86 4+3
When the engine first starts it must be kept running with light throttle. After a few seconds it will settle down and run fine at about 900 rpm. After about 2 minutes idle will pop up to 1100. Driving the car produces normal throttle response and normal idles at 700 to 800 rpm after warm up. Idle is high as the car comes to a stop and settles back to 700 to 800 rpm. There are no codes indicated and otherwise all seem normal. I replaced the IAC once to "solve" this problem but nothing changed. Any ideas would be appreciated. The corvette shop manual is no help.
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Joined: Dec 2000
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From: SE NY
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Re: Cold Idle problem on 86 4+3 (JOHN*99*)
When replacing the IAC you need to clean it's bore under the TB (clean the TB as well) and reset base idle to 450RPM, method on my site.
At that time you might recheck TPS voltage as well.
At that time you might recheck TPS voltage as well.
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Joined: Apr 2004
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From: Fairfax Virginia
Re: Cold Idle problem on 86 4+3 (JOHN*99*)
All things mentioned have been tried at least once with no effect but I dont mind trying again. I went to your web site and read your procedure for base idle adjustment. I noticed that you dont disconect the timing connector as mentioned in the GM shop manual. Does this make a difference? That connector is a bear to reach.
Could the temp sensor be involved with the problem since the idle pop up occurs after about 2 minutes of running?
Could the temp sensor be involved with the problem since the idle pop up occurs after about 2 minutes of running?
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Joined: Dec 2000
Posts: 90,675
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From: SE NY
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Re: Cold Idle problem on 86 4+3 (JOHN*99*)
You can use the field service diagnostics on my site to see if the coolant temp sensor is ok; if not the ECM won't go into closed loop mode.
Part of your cold idle problem could also the the "other" coolant temp sensor in the front of the ending, the one that feeds the cold start injector timer. I believe this is the one on the right under the TB.
Part of your cold idle problem could also the the "other" coolant temp sensor in the front of the ending, the one that feeds the cold start injector timer. I believe this is the one on the right under the TB.
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Joined: Apr 2004
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From: Fairfax Virginia
Re: Cold Idle problem on 86 4+3 (65Z01)
From what I read the cold start circuit is only active for 8 sec when the engine is cranking. I suppose it could activate late but that would still only last a few seconds. I do have a AutoXray scanner. I should check temp with the engine at ambient and not started (ignition on).
