Idle Speed/Throttle Actuator - Electronic: Description and Operation

ISC Servo 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.

Idle Speed Control Servo (ISC Stepper Motor):

Construction
The (IAC) servo consists of a motor, worm gear, worm wheel and plunger. A motor position sensor (MPS) is used to detect plunger position, and a closed throttle position switch is used to detect idle position. The worm wheel (attached to the motor shaft) is meshed with the worm gear on the plunger.

Operation
As the motor rotates, according to the signal from the ECU, the plunger extends or retracts. This actuates the throttle valve via the ISC lever. In this way, the idle speed is controlled by changing the throttle valve opening.

The Idle Air Control (IAC) servo adjusts the idle for air conditioning and automatic transmission loads and is used as a fast idle for cold start. The ECU uses the idle speed control (ISC) servo to make idle adjustments.