1992 Geo Prizm Engine racing than slowing down at startup

Tiny
PENDON
  • MEMBER
  • 1992 GEO PRIZM
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 80,000 MILES
My wife called me and said that when she started the car, the engine kept racing and than slowing down. I told her to shut the car off than try again. She did so and had the same problem. I told her I would check with my son who works on cars but he couldn't help. When I caled my wife back she told me it stopped and the car appears to be alright. Can You please tell me what would cause this to happen.

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Thursday, June 5th, 2008 AT 5:01 PM

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Tiny
BLACKOP555
  • EXPERT
Most likely cause is a faulty IAC module, it is what sets the idle on the vehicle and when the vehicle idles rough it is usually the IAC module causing that.

How it works is it allows a certain amount of air to bypass the closed throttle valve to limit the speed of the engine at idle.

Another possible cause could be a vaccum leak but is unlikely because she said it was running normally now.
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Thursday, June 5th, 2008 AT 8:38 PM

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