Idle Speed/Throttle Actuator - Electronic: Description and Operation

Typical Idle Air Control (IAC) Valve:

PURPOSE
The Idle Air Control (IAC) valve is used to control engine idle speed provides a dashpot function.

OPERATION
The IAC valve assembly meters inlet air around the throttle plates through a bypass within the IAC valve assembly and throttle body. The desired idle speed or air bypass is determined by the [1][2]Powertrain Control Module (PCM) and controlled by a duty cycle signal.

The IAC solenoid (part of the throttle body assembly) has an internal diode on some applications. If this diode is measured in crossed terminal position with a DVOM, there will be an incorrect or negative reading. It is important that the mating component and harness connectors be in the proper orientation.

The IAC controls:
- Cold engine fast idle
- No touch start
- Dashpot
- Over temperature idle boost
- Engine idle load correction