92 Civic idle speed variation

ken_in_kcJune 18, 2009

My daughters '92 Honda Civic idle varies from day to day. She says it often seems the vary with the air temperature. I have from time to time adjusted the idle up or down a little.

I understand that leaks in the vacuum hoses can affect idle speed as well as a number of sensors. Visually the small vacuum hoses look OK.

Anything I can check out myself realizing I have no particular skill or special tools? It seems to idle faster on warmer days and vice versa.


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It could be the idle speed is being automatically adjusted upward when the AC kicks in, or is turned on. If you have a carbureator, this is accomplished with a two step cam under the idle stop screw, or some other mechanical arrangement; If you have an IACS (idle air control system), the engine controller ajusts it for more air flow at idle with AC activated.

If the system adjusts the idle input upward and the AC compressor does not increase its load correspondingly (not working), the engine speed will increase more than desired.

There are other causes for variable idle speed such as worn cam shaft or clogged catalytic converter. Likely, the most expedient way to remedy this problem is to take the car to a qualified shop and get a set of diagnostics.

    Bookmark   June 18, 2009 at 4:36PM
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The AC wasn't on when this happened.

Turns out it was the PCV valve. Problem solved.

    Bookmark   March 16, 2011 at 8:32AM
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