This can happen if the idle control unit gets disconnected or goes bad. The default idle speed is then ~1700. It is a plastic box located in the firewall behind the air cleaner. The connector is on the bottom. Check that first.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma