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Fast idle
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bbanks
New User
| Posts: 1
| Joined: 07/09
Posted: 07/24/09
08:09 AM
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I have a 92 LT1 with 38,000 miles. About a year ago I had all gaskets and seals belts and distributer replaced. Shortly thereafter it started to idle at about 1800 to 2000rpm once it warms up. It also will run fine for awhile shut it off then start back up and it idles high then. I've had it looked at by somebody else he thought it was a hose, fixed it and it worked fine for a couple days then started doing it again. 
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Posted: 07/26/09
06:20 PM
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plug in a scan tool.... look at coolant temp sensor.. should be over 215F...
with the engine coolant up to temp... the IAC should be between 20 and 50 counts...
if it is below 20... you have a vacuum leak .. if it is above 50... you probably have a worn throttle shaft bore... or somebody has tampered with the base idle speed screw...
the throttle position sensor voltage should also be slightly below 1.0 volts.. but above 0.35.. i don't have the exact specs in front of me right now..
work the throttle a few times... while watching the TPS voltage each time it closes... it should return to the exact same voltage...
and if the thermostat is sticking open... so the coolant temp is too low.. the ecm will keep it at fast idle.. way over 50 IAC on the scan tool...
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