I've mostly worked on Chevys, and (IIRC) the target idle is dynamicly calculated to the MAP, CSS, MAF, IAT and CTS datastreams when TPS is 0. The Chevy Silverado Vortec PCM's like 575 rpm.
Maybe the old plugs caused a very very minor misfire and the CSS caught it so it raised RPM to cancel the loss out.
I'm not sure what would give the PCM reason to retrain itself after new plugs were installed tho?
Quote:
Originally Posted by Red
Why is your Cavalier idling at a lower RPM? Far as I know its a computer controlled vehicle, so its idle should be more or less hard coded into the ECU. Logically speaking, plugs shouldn't change your idle speed
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