IAC Valve Symptoms

Last year, I replaced my Idle Air Control valve because of stalling while idling. Could a defective IAC valve also cause excessively fast idle? Or, do I have to look elsewhere for the problem?

It could, but I would start by looking for vacuum leaks.

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Try rapping on the IAC valve with the handle of a screwdriver while the engine is idling.

If the idle speed changes, the IAC valve is faulty.

Tester

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