The Intake Air Control is a bypass airflow valve located on the throttle bodycontrolled by the engine computer.







It is a solenoid with a loaded plunger under spring tension and some dampened dashpot action. The engine computer looks at the PIP (tach) signal, along with some other parameters to determine the amount of air to allow by the throttle plate to maintain the air required for the engine conditions.


At idle, this device is pulsed against its spring and dashpot action so smooth control of the airflow is obtained. The computer continuously adjusts this flow rate to match the programs value in the idle tables, subject to modification for cold temp starts, deceleration actions, engine acc loads etc. Anything that causes the IAC not to follow input pulses at the required rate and movement will affect the idle speed of the engine the same as an unaccounted for air leak would cause. Note that the throttle body opening (throttle stop) must be set below the normal idle (but not tight closed) for the IAC to have complete auto airflow adjustment range.


This is the description of non adjustable idle speed because it is really controlled in the computer program. The hardware is there to operate to the correct idle as specified in the computer program.