Idle Speed Control System

The ISC system provides the following four modes of control:
1. Start Control-- The throttle valve opening is controlled to optimum position forstart according to the engine coolant temperature (RPM feedback control).
2. Fast Idle Control-- When the idle switch is On, the engine speed is controlled to a target RPM according to the engine coolant temperature (RPM feedback control). When the idle switch is Off, the ISC servo is actuated to move the throttle valve to a target opening position according to the engine coolant temperature (target opening control).
3. Idle Control-- When the A/C switch is turned On, or on models with automatic transmission the selector lever is shifted from N to D, the system causes idle speed to increase to the target RPM according to the load (RPM feedback control). When the electrical load changes in such an occasion as turning the a/c On, a time lag exists before the RPM feedback control becomes effective. During that period, a control to adjust to the target RPM (throttle valve opening) works to prevent engine speed drop.
4. Dashpot Control-- The system provides dashpot control according to deceleration conditions to alleviate shock at deceleration.