Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Speed Control (ISC) Servo Circuit:

The Idle Speed Control (ISC) servo, located on the throttle chamber regulates and controls the idle for the loads placed on the engine.
The ISC 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 will supply Voltage in one polarity direction, which will turn the motor in a particular rotation. Connected to this motor's shaft is a screw that when turned, either opens the passage or closes the passage (depending upon rotation) 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 speed control (ISC) servo to make all of the adjustments to the idle.