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After starting my 98 metro 1 liter the idle increases in less than a few minutes until the engine is racing so fast I have to shut it down, help?

Notice the high idle yesterday. When I got it home idle was still high even though it was fully warm. Tried to rev it and back off but it just increase idle more.

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  • Cars & Trucks Master
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Generally speaking, the only way for the idle speed to increase is if extra air is getting past the throttle plate.
So that could include the throttle plate sticking open, the idle air control valve not closing, or a vac leak somewhere such as a hose or gasket.
If you can cover the throttle body with something and the engine still runs at a high speed there is a large vac leak somewhere.

Posted on Jan 22, 2013

  • 6 more comments 
  • Scott Magno Jan 22, 2013

    Good point covering the trottle body (quickly and briefly) to see if it starts to chock off. One other thing I should have added is that I unplugged the IAC electrical and started but it was still at very high RPM. I thought unplugging the IAC would cause something to happen unless it's busted? Does the IAC allow air in where I can not see it?

  •  Stephen
    Stephen Jan 22, 2013

    Well it opens a port in the throttle body. And unplugging it won't matter if it is already open too much. It is an electric motor that opens and closes the port.

  • Scott Magno Jan 22, 2013

    Thanks. One more then I'm going to diagnose some more - what is the risk of removing the IAC, anything I need to be aware of before removing?

  •  Stephen
    Stephen Jan 22, 2013

    No risk I know of. As long as you don't start the engine with it removed.

  • Scott Magno Jan 22, 2013

    Skycheif2001, thanks so much for your help so far. I removed the IAC and turns out the piston is not retracting far enough back into the IAC housing. I can not push it back far enough with hand pressure. Before removing the throttle arm was not returning back leaving the throttle valve open evident by the fact the the throttle arm was not coming back and touching the idle adjustment screw. More evidence that the IAC was keeping the trottle open. So, either the IAC is busted or the mechanism iside the IAC is stuck in position and not getting signa from the sensor(s) telling the IAC to adjust (TPS, others?). I did try cleaning the IAC piston but it won't move far enough. Thoughts from here?

  •  Stephen
    Stephen Jan 22, 2013

    The photo of the part looks like it is an idle speed control rather than air control. Even tho they call it idle air control. It is also very expensive to buy. I would probably drive it without the control to see if the throttle works correctly. If it does, you might be able to find a used part. The basic purpose of the part is to raise base idle to cover extra engine load from the transmission and other components. Running the car without it should turn on the check engine light so you can't leave it off forever.

  •  Stephen
    Stephen Jan 22, 2013

    You may be able to raise base idle a notch or two for the experiment.

  •  Stephen
    Stephen Jan 22, 2013

    The computer also raises base idle speed when the engine is cold.

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check all your vacuum hoses and the throttle body itself for a vacuum leaks if the hoses replace as nessasary if to check for throttle body get can of carb cleaner and spray around base of throttle body and sides not in it if idle raises you have a vacuum leak goto a good parts store and ask for a rebuild kit don't goto auto zone or advance they don't carry them

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SOURCE: This is a 1997 Geo Metro with 1.3L engine. It

take off your idle air control motor and clean it with carb cleaner sounds like clogged and check your idle screw on the throttle body where wire from pedal connects to throttle body make sure it is not got something making it stick or push down cable and make sure the throttle body not dirtyl spray carb cleaner in it sometimes when dirty let in excess air and causes extra gas be used and high idle try these see if fixes it

Posted on Sep 24, 2010

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