engine revs up and down - Engine Troubleshooting


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mrc55
User

Jan 23, 2014, 2:43 PM

Post #1 of 3 (1522 views)

engine revs up and down	Sign In

1996 Honda Civic, 1.6, 249,000
When car warms up engine starts a rev/decline thing and won't stop. Revs up and down up and down. If you take it out of park it stops. Only change is I put on a cold air intake.

Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jan 23, 2014, 3:04 PM

Post #2 of 3 (1512 views)

Re: engine revs up and down	Sign In

Check for vacuum leaks. Don't mess with the idle air screw. Also make sure the coolant is in good condition. You could also have a problem with the idle air control valve assembly. You can tell by putting your finger over the idle air control intake port in the throttle body before the throttle plate with the engine running. If the idle comes down, you have a problem in the idle air control system.

The reason the engine is idling that way is because you have unmetered air getting into the intake. When the idle gets too high in park or neutral the engine computer turns off the injectors. Then the cycle repeats.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

Hammer Time
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Jan 23, 2014, 3:49 PM

Post #3 of 3 (1497 views)

Re: engine revs up and down	Sign In

In addition to what DS suggested, some of these Hondas were equipped with a deceleration valve that can leak internally and also do that.

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