Cold/Warm Engine Speed Controls

Auxiliary Air Regulator Valve:

COLD ENGINE
The intake collector mounted air regulator is used to provide a cold fast idle. The unit consists of a shutter wheel and an electrically heated bimetallic strip. When air temperature is cold, the bimetallic strip causes the shutter wheel to open. When open, the shutter wheel allows air to bypass the throttle plate, raising idle speed. Once the engine is started, voltage is applied to the heater coil wrapped around the bimetallic strip. When heated the strip begins to close the shutter wheel which in turn closes the bypass air passage.

Idle Air Adjusting Unit:

WARM ENGINE
The idle air adjusting (IAA) unit is mounted on the rear of the left intake collector. The unit consists of the auxiliary air control (AAC) valve and the fast idle control device (FICD). Both units control idle speed by modifying the amount of air allowed to bypass the throttle plates. The AAC is constantly pulsed by the ECU at a frequency of approximately 160 hz. The ECU varies the duty cycle ("On" time versus "OFF" time) to raise or lower the idle as needed. The FICD is a solenoid valve that opens/closes an air passage and is used by the ECU to adjust the idle speed to instantly compensate for engine load.

Idle Speed Control System:

Refer to chart for AAC operation.