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high idle at start

Old 11-03-2018, 07:56 PM
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skip myles
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Default high idle at start

my 85 will idle at 1500 to 1900 when first started i can turn it off and restart it will idle around 800 i doesnt matter the temp doesnt do it every time some time it will crank at about 1100 then drop to 750 when warm

thanks for any help

Last edited by skip myles; 11-03-2018 at 07:59 PM.
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Old 11-03-2018, 11:05 PM
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billschroeder5842
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I'm not sure whats wrong? These cars (the L98) will have a higher idle when first started then drop to the idle specification of about 700-800.

What is happening that makes you think your car is not performing correctly?
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Old 11-04-2018, 01:09 AM
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aklim
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Originally Posted by billschroeder5842 View Post
I'm not sure whats wrong? These cars (the L98) will have a higher idle when first started then drop to the idle specification of about 700-800.

What is happening that makes you think your car is not performing correctly?
Does your's do 1500 to 2000, assuming his tach is right? I don't think mine does but it is modified so all bets are off.
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Old 11-04-2018, 05:22 AM
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From a cold start, mine idles (an 86) from 1500-1700 rpms until the engine oil temp is up to around 160-170 degrees or above. Once it's to temp it will drop to around 700 rpms when you stop and the forward motion gets to zero mph. If I'm running some errand when I restart and it's still in operating temp it will immediately from to around 700 rpms when you stop.

On mine, it all appears to be related to operating temp. Just my info.

Last edited by hcbph; 11-04-2018 at 05:24 AM.
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Old 11-04-2018, 12:22 PM
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If you scan the ECM you might see what the desired idle is and see if it is trying to compensate for something.
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Old 11-04-2018, 03:35 PM
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Hook a test light up on your Cold Start Injector and see if it is the cause of the higher RPM. When it is cold enough it should start your car and make it idle a bit faster while warming up. My car idles fast when really cold so it is probably getting the extra fuel from the 9th injector causing the idle to speed up.

If you have a temperature sensor going bad it can cause the Cold Start injector to run when not needed. This sensor makes starting more difficult and some times darn near impossible as it can flood the engine. The sensors can be checked by measuring the resistance and referring to a chart that shows the temperature at a specific resistance. This could clearly have an affect on your Corvette's ability to start and idle normally.

Check for any vacuum leaks in the engine area, the EGR has a Vacuum solenoid near the thermostat and I frequently find leaks there. Go through your engine and verify that your vacuum system is set up normally and not leaking. My EGR had gone bad and I found an open vacuum line on my car. Cut 1/2" off the existing lines if you have the room to do so and make a new solid vacuum connection. When my EGR was bad the idle was off as well, afterwards it idles so smoothly.

I wish you the very best in solving this little mystery. I hope you find it without any problems.
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