Glenn is on the ball, this rotary valve is closed by a bi-metal spring, that can get gummed up. When it is cold the spring opens the rotary valve, to allow extra air for a faster idle speed,when the ignition is turned on, the electric heating windings heat the spring to close the valve.
An easy way to test, is to pull the AACV hose that runs from the left hand side of the black box on the throttle bodies. When the engine is cold, you should be able to blow through the valve. Then turn on the ignition, don't start the engine, after a few minuits the valve should heat up, to close the valve, and you should not be able to blow through it.
Harvey.
