Where is it? Mounted to the side of the plenum with a rubber pipe connected to the air filter side of the throttle body (center of picture)

What is it? The IACV is a unipolar winding stepper motor connected to an air bleed valve. By grounding a combination of 4 control inputs the valve can be proportionately opened or closed.

What's it for? The ECU controls the idle speed by sending a 4 bit code to the IACV this in turn bleeds air past the throttle spindle thereby bleeding air into the plenum. The idle speed will be raised during engine warm up (the ECU monitors the engine Coolant Temperature Sensor), and during idle, will continually trim the amount of air passing into the plenum. On engine switch off, the ECU will setup the IACV for the next engine start.