Idle Speed Control System

PURPOSE
The Idle Air Control System allows for precise control of the engine idle during cold, warm and high load conditions.

OPERATION
Idle speed is controlled by fine adjustment of the amount of air allowed to bypass the throttle valve.

Three different devices, all part of the Idle Control System, are used to control engine idle. The devices are:

1. Idle Air Control Valve-Air Regulator (IACV-Air Reg)
^ Used to provide additional by-pass air during cold engine operation. Allows cold fast idle. Is activated by 12 VDC.
2. Idle Air Control Valve-Fast Idle Control Device (IACV-FICD).
^ Used to provide a small amount of idle-up when the A/C compressor is turned on. Is activated by 12 VDC.
3. Idle Air Control Valve-Auxiliary Air Control (IACV-ACC) Valve.
^ Used to provide fine control of the engine idle during normal conditions. Is activated by a duty cycle signal from the Engine Control Module (ECM) at a rate of 100 - 200 Hz.