Circuit/System Description

The throttle body assembly uses an idle speed control (ISC) system that contains motor, throttle position (TP) sensor, motor position sensor, and an idle switch. The ISC system is used to control engine speed at idle. The engine control module (ECM) uses high and low control circuits to control the ISC motor. A 5-volt reference and low reference supplied by the ECM is shared by both the TP and motor position sensors. The TP and motor position sensors each have a signal circuit to feedback voltage to the ECM. The ECM commands the ISC motor by pulse width modulating the voltage on the high and low control circuits to adjust the throttle angle for idle speed control. The motor position sensor is used by the ECM to monitor the position of the ISC motor for idle operation. The TP sensor is used by the ECM to monitor the position of the throttle blade. An idle switch is used by the ECM to monitor when the throttle blade is at it rest position to allow the ISC motor to control idle operation. With the throttle blade at the rest position, the idle switch will be closed. When the throttle blade is opened, the idle switch will be open.

The ISC system consist of the following circuits:

• A 5-volt reference
• Idle motor high control
• Idle motor low control
• Idle motor position signal
• Idle motor switch signal
• Low reference
• Throttle position sensor signal