1988 Chevy Truck High Idle

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Engine Performance problem
1988 Chevy Truck V8 Four Wheel Drive Automatic 113000 miles

Recently my truck has developed a high idle problem. The problem is that the engine idles fast and I have to step on the brake firmly at stop signs to hold it from creeping forward. It runs good at highways speeds otherwise. Also, if I put it in park, the engine will idle down somewhat but when I put it in gear the engine will stutter for a few seconds and then idle up again. And, I'm pretty sure the torque converter is not locking up like it's supposed to at speed. I checked the vacuum lines and they look OK. I sprayed carb cleaner around the TBI and vacuum lines and the idle wasn't affected. Coincidentally (or not) it this all started shortly after I added some STP carb and fuel injector cleaner to the gas. I've driven it maybe 150 miles since then and have added more gas to the tank with no change in the symptoms. Any ideas before I take it in?

Found the problem - it was the coolant temperature sensor. It was reading -11F and causing a rich fuel mixture. And it would't allow the torque converter to lock up.

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have the same problem?
Tuesday, May 27th, 2008 AT 11:31 AM

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There are a few things that couold cause this, tps, idle air control valve or ignition timing. These trucks have a problem with the shaft in the distributor cracking from the heat and causing the reluctor wheel to float. A easy way to check this is to check ignition timing and if it changes then you know thats the problem. To check tps you need a scan tool to watch the data. Let us know how you make out.

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Tuesday, May 27th, 2008 AT 11:41 AM

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