Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Speed Control System:

The Idle Speed Control (ISC) Systems Primary function is to regulate the control of the idle to adjust for the loads placed on the engine. The ECU uses several sensor inputs to determine the operating condition of the engine and the loads being placed on it. The system adjusts the idle for air conditioning and automatic transmittion loads and is used as a fast idle for cold start. The ECU uses the idle speed control (ISC) servo to make all of the adjustments to the idle.

Idle Speed Control Servo (ISC Stepper Motor):

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