Idle/Throttle Speed Control Unit: Description and Operation

Fig. 6 Digital electronic fuel injection idle speed control:

Vehicle idle speed is controlled by an electrically driven actuator (ISC), Fig. 6, which changes the throttle angle by acting as a moveable idle stop. Inputs to the ISC actuator motor come from the ECM and are determined by the idle speed required for the particular operating condition. The electronic components for the ISC system are integral with the ECM. An integral part of the ISC is the throttle switch. Position of the switch determines whether the ISC should control idle speed or not. When the switch is closed, as determined by the throttle lever resting upon the end of the ISC actuator, the ECM will issue the appropriate commands to move the ISC to provide the programmed idle speed. When the throttle lever moves off the ISC actuator from idle, the throttle switch is opened, the ECM extends the actuator and then stops sending idle speed commands and the driver controls engine speed.