What Is An Idle Air Control Valve?

Sherry D brought a 2002 Honda Civic to my shop that she recently purchased. She told me that the car would not idle, the engine surged up and down constantly. She just purchased the car, and wanted to know if I could fix the car. She told me that the car sat for several years and that was pretty much all I needed to know. In the pictures shown it is not too hard to figure out which idle air control valve is the old one. With this design Honda uses a round type barrel valve to control the amount of air that is fed into the engine upon cold start. Normally when the valve is functioning correctly as it should the engine has ample air available upon cold start. When the engine is first started the tachometer moves up to around 1200 RPM (revolutions per minute) and as the engine warms, so does the coolant that passes through the valve. As this happens a little spring heats up as well and it slowly rotates the barrel  type shaped  valve. Then the valve reduced the amount of air allowed to enter the intake and then the idle is reduced to around 750 RPM after the engine is fully warmed up.  In this case the valve was stuck in the middle position. Based on input from the engines coolant temperature (cold) fuel metering or duration can not be properly determined and in Sherry’s case that is where the source of the surging came from.  Replacing the Idle air control valve corrected her vehicles issue.

New Idle air control valve

New Idle air control valve

Old Idle air control on the right . New valve on the left.

Old Idle air control on the right . New valve on the left.

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