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Questions and Answers

Geo High Idle

Q. I have a 1992 Geo Metro 3cylinder with 72,000 miles. Once the engine gets warm and I slow to a stop the motor idles fast and has an RPM surge up and down. If I give it a little gas or let the clutch out some to put a small load on the motor the surge stops and

the higher idle remains. But the next time I come to a stop the surge returns. I have checked all of the vacuum lines as that sometimes causes this type of problem. I'm new to the Geo world and am a novice shade-tree mechanic. Any advice will be gratefully appreciated.

Jeff

A. Chances are the problem is in the Auxiliary Air Valve or Idle Speed Control solenoid valve.

The Auxiliary Air Valve is the "choke" of a fuel injected engine and gives you the high cold idle. When the coolant temperature reaches about 140 degrees, it closes and you have normal idle. If the valve does not close, you will get the symptoms you describe.

The ISC controls idle speed by a pulsed signal from the ECU which opens and closes a valve. The ISC is easily checked with a scan tool. Since most DIYs don't have this tool, it's best to take it to a shop to have it checked.t

Information provided courtesy of ALLDATA

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