Cold/Warm Engine Speed Controls

Idle Air Control Valve-FICD:

WARM ENGINE
The idle air adjusting (IAA) unit is used by the ECU to control warm engine idle speed. The IAA unit is mounted on the back of the intake air plenum. The IAA consists of the auxiliary air control (AAC) valve and the fast idle control device (FICD). Both units control idle speed by controlling the amount of air allowed to bypass the throttle valve. The AAC is used by the ECU to control normal curb idle. The FICD is used by the ECU to compensate for the added load of the air conditioning compressor.

Auxiliary Air Regulator Valve:

COLD ENGINE
The air regulator is mounted on the air intake plenum. The air regulator is used to provide a cold fast idle to the engine. It consist of a rotary shutter wheel that is controlled by an electrically heated bimetallic strip. When engine temperature is low, the bimetal strip allows the rotary shutter to open. With the shutter open, a relatively large amount of air is allowed to bypass the throttle plate, causing a fast idle. Once the engine is started, voltage is applied to the heater which slowly causes the bimetallic strip to close the shutter. With the shutter closed, the air bypass channel is closed lowering the idle speed to curb speed. The IAA then takes over controlling the idle speed.