My friend has a Mercury Mystique and it idles too fast. What should he have done to correct?
Clean the throttle body and IAC valve, they can have a build of carbon effecting the idle. Your local auto parts store will sell specific cleaner to do the job. Search youtube for howto's. If that doesn't work, check for vacuum leaks.
What about the Throttle Position Sensor?
That can't be cleaned, but if faulty will usually trip a code /CEL.
The problem is most likely the Idle air control valve, If it is stuck open the engine will idle too fast!
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