Idle Speed Control System Description. Chevrolet Joy 2008

For 1990-2009 cars

### Purpose

The idle speed control (ISC) system delivers improved throttle response and greater reliability. The ISC system consist of the following components:

• | A throttle body

• | An engine control module (ECM)

### Throttle Body Assembly

All the throttle body components are integrated into the throttle body assembly. The throttle body assembly consist of the following components:

• | The throttle body

• | The throttle blade

• | The throttle position (TP) sensor

• | The idle switch

• | The idle speed control (ISC) motor position sensor

• | The throttle actuator motor

The throttle body functions similar to a conventional throttle body with the following exceptions:

• | An electric motor opens and closes the throttle blade.

• | The throttle blade is spring loaded in both directions with the default position slightly open.

The position sensors are used to determine the throttle blade movement. The TP sensor provides the engine control modole (ECM) with a signal voltage proportional to the throttle blade angle.

### Throttle Body Circuits

The throttle body consists of the following circuits:

• | The idle speed control (ISC) motor high control

• | The ISC motor low control

• | The idle switch signal

• | The ISC motor position signal

• | The 5-volt reference circuit

• | The throttle position (TP) sensor signal

• | The low reference

### Engine Control Module

The engine control module (ECM) receives an ON signal from the idle switch when the throttle is at idle and receives an OFF signal from the switch when the throttle is open. The ECM achieves throttle positioning by providing a pulse width modulated (PWM) voltage to the motor. The motor is a direct current DC type of motor. At idle the motor controls the throttle blade angle between 0-24 degrees. The idle speed is controlled mechanically by a cable above 24 degrees.

### Limp Home Mode

The limp home mode allows the throttle blade to remain in a fixed position for limited throttle. The throttle blade angle is fixed between 5-6 degrees.