Purpose
The idle speed control (ISC) system delivers improved throttle response and greater reliability. The ISC system consist of the following components:
| • | 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 position (TP) sensor |
| • | 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 ISC motor position signal |
| • | The 5-volt reference circuit |
| • | The throttle position (TP) sensor signal |
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.
