The engine is pulsing & hesitating. While idling at about 800RPMs the engine will jump up to 1400RPMs and then down to 300RPMs and then it will go back to normal. Some times the engine dies. While driving the car sometimes hesitate - this was the first symtom. I thougt that it may gave been a transmission slipage problem until I noticed the idling issue. There is no engine warning light. I assume it is a sensor issue, but I don't know how to track it down or repair it. The carr is a 2002 Pontiac Grand Prix w/ 95,000 miles. Any suggestions?

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2002 Pontiac grandprix 3800