Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Control Valve:

Throttle Body:

PURPOSE
The purpose of the idle air control (IAC) valve is to provide a way for the ECM to control engine idle speed. The IAC valve is installed in the throttle body and works by controlling the amount of air that bypasses the throttle plate.

DESCRIPTION
By moving a conical shaped valve, known as a pintle, towards its seat, the IAC valve reduces the bypass air rate which in turn causes engine speed to be reduced. Conversely, by moving the pintle away from its seat, The IAC valve increases the bypass air rate and increases the engine speed. If the ECM detects that the idle speed is not correct, it will command the IAC valve to bypass more or less air to regulate idle speed.


OPERATION
The ECM monitors battery voltage, coolant temperature, engine rpm, vehicle speed, throttle position and auxiliary engine loads in determining what commands to send the IAC valve. The IAC valve moves by taking a series of steps known as "COUNTS". The higher the number of counts, the farther the pintle is moved from its seat and more air is bypassed.



DIAGNOSTIC NOTES:
If the IAC valve is disconnected and reconnected with the engine running, the idle rpm may be wrong. In this case, the IAC has to be reset.

When servicing the IAC, it should only be disconnected or connected with the ignition OFF. This will keep from having to reset the IAC. If the IAC valve needs to be reset, depress the accelerator slightly and start the engine. Hold the throttle steady while the engine runs for about 5 - 10 seconds, then turn engine "OFF" for 10 seconds. IAC valve position should be reset.

For diagnosis and testing procedures, see COMPUTERIZED ENGINE CONTROLS.