Idle Speed Control System

Idle Air Control (IAC) System Inputs And Outputs:

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 via the Idle Air Control Valve-Auxiliary Air Control Valve (IACV-AAC). The IACV-AAC Valve repeats ON/OFF operation according to the signal sent from the Engine control Module (ECM). The Camshaft Position Sensor detects the actual engine speed and sends a signal to the ECM. The ECM then controls the ON/OFF time of the IACV-AAC valve so that engine speed coincides with the target value memorized in the ECM. The target engine speed is the lowest speed at which the engine can operate steadily. Optimum values stored in the ECM are determined by taking into consideration various engine conditions, such as warming-up and during deceleration, fuel consumption, and engine load.

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

^ 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 Volts DC.

^ 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 Volts DC.

^ 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 ECM at a rate of 100 - 200 Hz.