Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Control (IAC) Motor Circuit:

Purpose
The Idle Air Control (IAC) servo maintains idle speed by compensating for loads placed on the engine.

Location
The IAC is located on the throttle chamber.

Operation
The IAC servo is a stepper motor that regulates the amount of air taken in through the bypass circuit of the intake manifold by opening and closing the servo valve located in the air passage. The ECU supplies voltage in one polarity direction, which turns the motor in a particular rotation. The motor shaft is connected to a screw that when turned, opens the passage by moving the pintle. When the ECU reverses polarity, the passage is closed in the same manner.

The ECU uses several sensor inputs to determine the operating condition of the engine and the loads being placed on it. The ECU adjusts the idle for air conditioning and automatic transmission loads, and controls fast idle for cold start. The ECU uses the idle air control (IAC) servo to make all of the adjustments to idle speed.