Q: My 1999 Pontiac Sunfire coupe is doing something something I can't easily explain. The car has 240,000 km on it and it has the stock engine, although I think I bought it with a K filter charger.

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First thoughts are that the stepper-motor (which controls the idle speed) is faulty. That would explain both the high idle at low engine temps and the stalling and stumbling as you roll to a stop.