1997 Oldsmobile Cutlass Supreme mileage: 115,000. On cold starts, the idle speed is between 2400-3000 rpm. My local GM dealer did a computer diagnostic and replaced the PCM. Still had the problem, and they said it was probably the idle air control valve. That has been replaced too, but the problem persists. One other thing I have noticed is that with each new part, the idle speed is somewhat better but then progressively gets worse. Any ideas?
Your car is equipped with a computer controlled engine management system. An independent auto service center can scan your computer for fault or error codes. The information should pinpoint the malfunctioning components. If a major tune-up has not been done recently, this could be the cause of your problem. Replace the spark plugs, plug wires, fuel and air filters, etc. Also, replace the oxygen sensor. In addition, service the fuel injection system. Clean the carbon deposits from the throttle bore and idle passages.