What does an Idle Air Control (IAC) valve do?
– The purpose of the IAC valve is to allow the ECU to control an additional amount of air to enter the engine without touching the throttle. It’s basically an electronically-controlled vacuum leak that allows the ECU to control idle speed. The IAC valve consists of a stepper motor and a pintle. The stepper motor is controlled by the ECU, and the motor moves the pintle towards or away from a seat. The further the pintle is from the seat, the more air is being allowed into the engine. The ECU can raise the idle speed when the engine is cold, or maintain a given idle speed when an AC compressor turns on by allowing more air into the engine. – To get the IAC motor to work best for you, the blades on the throttle body should be set so that the IAC valve is barely open while idling. This will allow the IAC valve all the room to open up that it will ever need. – If you are running in Alpha-N mode, use of an IAC motor is not recommended. Because fueling in an Alpha-N calibration is dependent o
