Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Control (IAC) System:

Idle Air Control Valve:

IAC System:

Engine idle speed is controlled by the Powertrain Control Module (PCM) through the Idle Air Control (IAC) valve mounted on the throttle body. The PCM sends voltage pulses to the IAC motor windings, causing the IAC pintle to extend or retract a given distance (number of steps or counts) for each pulse. The pintle movement controls the air flow bypassing the throttle valves, which in turn, controls engine idle speed.
^ Engine idle speed is a function of total air flow into the engine based on IAC valve pintle position + crankcase ventilation valve flow + throttle valve opening + calibrated vacuum loss through accessories.
^ Controlled idle speed is programmed into the PCM, which determines the correct IAC valve pintle position to maintain the desired idle speed for all engine operating conditions and loads.
^ The minimum idle air rate is set at the factory with a stop screw. This setting allows enough air flow by the throttle valves to cause the IAC valve pintle to be positioned a calibrated number of steps (counts), from the seat, during controlled idle operation. The throttle stop screw is covered with a plug at the factory following adjustment.

NOTICE: Do not try to remove the plug and readjust the stop screw. Misadjustment may result in damage to the IAC valve or throttle body.

^ If the IAC valve is disconnected and reconnected with the engine running, the idle speed may be wrong. In this case, the IAC valve is reset by depressing the accelerator pedal slightly, starting and running the engine for five seconds, then turning the ignition "OFF" for ten seconds.