C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

1989 C4 Hi Idle

Old 07-08-2019, 05:40 PM
D Maners
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Default 1989 C4 Hi Idle

I fire the car up and it idles about 1100 rpm as it warms up the ideal keeps going up. After 5 minutes it is idling at 1500 rpm. I floor it a couple times to see if it drops-no go. Does the ECM control that?
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Old 07-08-2019, 06:07 PM
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huge vacuum leak.

may as well check for it using the cigar method cause its fun

then after fixed search the minimum idle procedure and follow that and u should be good to go
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Old 07-08-2019, 08:16 PM
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Mine does the same thing occasionally.
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Old 07-08-2019, 09:17 PM
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Originally Posted by VikingTrad3r View Post
huge vacuum leak.

may as well check for it using the cigar method cause its fun
Viking is correct on both accounts. Grab some beer, smokes and a couple of buddies. You will locate your problem on the first light and first beer. Pretty simple and stupidly accurate method.
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Old 07-09-2019, 04:25 AM
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When this happens, pull a hose off the manifold and block it. See what happens. If no changes put it back, When are are done, spray brake cleaner around the gaskets. See what happens. Any change and that is the looking point. I would prefer to do this with a scanner to see what the vital signs are based on the ECM and what it sees.
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Old 07-09-2019, 12:31 PM
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Would also do this with a scanner hooked up to see what the ECM is seeing. IAC counts, TPS voltage at idle, target idle RPM all are in the datastream.
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Old 07-09-2019, 01:49 PM
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A failing TPS can cause idle creep.
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