Idle Problem

When I turn my car on and let it idle it will rev up then drop down and then rev up and so on. It will only do this when it is cold out, but it doesn't always do it. What could be the problem?

When I turn my car on and let it idle it will rev up then drop down and then rev up and so on. It will only do this when it is cold out, but it doesn't always do it. What could be the problem?


Well you could have done a search as every 3rd thread or so is about irratic idles...but the main 3 causes are plugs, o2 sensors, or vacuum leaks. Also could be the valve on your throttle body.

having the same problem, just noticed it yesterday.

Glad this post is on the first page,

How does one decifer Exactly why its doing what its doing.. ?

Change your spark plugs...costs about $6 if you know how to do it...very simple.

Clean your throttle body $3..do a search for instructions and cleaner...

Pop the hood and follow all vacuum lines, listen for air leaks...you can pressure test, or you can put soapy water on all tubes and check for bubbles.

bad 02 sensors typically will make your ECU throw a CEL(check engine light) they will also cause your gas mileage to go down, and for you to lose power(unfortunantly, so will all the other possible causes)

Try all that...and see if anything works. All for about $9.