Idle Speed Control System

This system controls the minimum throttle position by means of ECM and idle speed control actuator (ISC actuator) for the following three purposes.
- To keep the engine idle speed as specified at all times The engine idle speed can vary due to following reasons.
* Load applied to engine (when electric load is applied, automatic transmission is shifted to "R", "D", "2" or"L" range, A/C is turned ON, etc.)
* Variation in atmospheric pressure
* Change in engine itself with passage of time
* Other factors causing idle speed to change
- To improve starting performance of engine
- To compensate air/fuel mixture ratio when decelerating (Dash-pot effect)

OPERATION
The ISC actuator opens and closes the throttle valve according to signals from ECM. When a normal rotation signal is sent from ECM to the SC actuator, the plunger expands to open the throttle valve and when a reverse rotation signal is sent, the plunger contracts and the throttle valve moves toward closing position by the return spring force. How much the throttle valve opens or closes is controlled according to the time during which electricity is charged (signals are transmitted) from ECM to the ISC actuator. That is, the longer the time is, the larger the valve movement is, whether opening or closing. Using signals from various sensors and switches, ECM detects the engine condition and controls the engine idle speed and minimum throttle valve opening by running the ISC actuator in normal direction or in reverse direction and stopping it.