when at idle the rpms increase and decrease dramatically

1986 HONDA PRELUDE
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NOTTUH
  • MEMBER
  • 1 POST
hello,it is fuel injected.my question is a diagnosis problem...when at idle the rpms increase and decrease dramatically and at a fast rate.i checked for a vacuum leak any thoughts?/
May 13, 2008 at 2:45 PM
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SQM
  • ✓ASE Certified Mechanic
  • 6,383 POSTS
  • ASE Certified Mechanic
Hello,

This issue is likely a faulty idle air control valve. Honda calls it the fast idle valve.
It is located on the intake manifold (see diagram).
Over time the valve can accumulate dirt and debris and create idle issue like you are experiencing.
Sometimes cleaning out the valve can improve the idle.

https://www.2carpros.com/articles/idle-air-control-valve-service

I have attached diagrams and the test procedure for the valve.

Please let me know if you have any questions.
Thank you.
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Oct 27, 2021 at 9:53 AM
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