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Variable RPM's. What controls idle?

Tiny
TAMMYP
  • MEMBER
  • 1998 HONDA CIVIC
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 129,000 MILES
I just bought a 1998 Civic with 129,000 miles on it that had been sitting undriven for 18 months. After the car warms up, the idle speed jumps from 400rpm's to 1700rpm's and back down to 400rpm's repeatedly and the engine makes a constant "revving" sound.
No matter how long the car runs, this problem continues and I am unable to "kick it down".
What could be the problem?
Thanks Guys!
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Monday, May 24th, 2010 AT 4:48 PM

1 Reply

Tiny
SQM
  • MECHANIC
  • 6,383 POSTS
Hello,

It sounds like a faulty idle air control motor. This will cause the car to have erratic engine speed. Have had the car scanned for codes?

https://youtu.be/dPOrNy-Y9Ng

You might find this article helpful:

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please let me know if you have any questions.

Thank you.
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Thursday, July 15th, 2021 AT 9:08 PM

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