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Low Idle and stalling

CHEVY C1500 1993 V8 5.7 L Truck has over 200,000 miles but the engine only has around 500 miles on it.

My truck runs great except for when it first starts and when I drive really slow (i.e. pulling into a parking spot, coming to a stop at a stop light/sign, sitting in a drive thru). It has a rough idle, and many times I have to put it in park and give it a little gas to prevent it from stalling. I’ve replaced the IAC which improved this issue dramatically but it still idles rough when it first starts and when I come to stop the RPMs go wonky, it will either correct itself, or it will stall. The engine has been rebuilt within the last 6 months. It has a new throttle body and TPS. New O2 sensor and a bunch of other sensors.

If anyone has any idea as to what it could be I would greatly appreciate it.

What year? How many miles? What engine?

Help us out a bit here and we’ll try and help you.

Try unplugging the electrical connector for MAP sensor, and then see how it starts/idles.


Yeah, that edit still didn’t say what engine… 350, 305, 4.3 V6…Or how many miles?

It sounds like it is running a little lean and/or the idle rpm is set too low. Have you checked for engine computer diagnostic codes? Your truck probably uses a flashing light method to read out codes rather than the fancy computerized scanners plugged into the obd ii port newer cars use, but it still provides diagnostic codes I expect. You might as well use that information, since it comes with the truck. If there are no codes, lots of possibilities for these symptoms, my guess is you’ve got a vacuum leak somewhere. Air is getting into the intake manifold using a path that isn’t allowed, bypassing the map sensor and throttle plate. The pcv system and the brake booster are two places to ask your shop to check.