Idle Air Control Valve

Step by step explanation on how an automotive idle air control valve works, though various manufacturer's create different styles of valve, the concept is the same.

Step 1 - The idle air control valve is located on the throttle bore (in most cases) and is designed to adjust engine air intake at idle which controls the engine idle speed. The PCM receives feedback data from various sensors to send output signals designed to adjust the air passage open or closed which adjusts the engine idle speed. At engine speeds above idle, the valve is not used and does not effect the engine. Engine idle speeds are not adjustable.

Idle Air Control Valve (Appearances Vary)

Step 2 - Internal air ports are used to regulate the volume of air allowed to pass through the valve. Some valves feature a coolant passage used to heat the valve for improved economy. These ports are sealed using a gasket which prevents the valve from leaking.

Air and Coolant Passages

Step 3 - Air passage bypass ports are used to route air past the butterfly and through the idle air control valve.

Throttle Bore Air Passages

Step 4 - Because of the massive amounts of air processed through the valve a condition called "coking" develops which can inhibit proper operation of the valve. This valve should be cleaned (serviced) whenever a tune up is performed.

Coking Condition

Helpful Information

When an idle air control valve fails it can cause the engine to idle erratically and even stall. Sometimes a weak idle air control motor will can cause engine problems without triggering a MIL (check engine) light. Inspect vacuum lines when servicing the idle air control valve and replace any that are broken or dilapidated.


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