Idle Up Control Valve: Description and Operation

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.

Fig. 57 Auxilary Air Control Valve:

WARM ENGINE
The idle air adjusting (IAA) unit is mounted on the back of the intake collector. The unit consists of the auxiliary air adjusting (AAC) unit 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 cycled on and off by the ECU at a frequency of approximately 160 hz. By controlling the duty cycle ("ON" time and "OFF" time) of the pulse, the ECU is able to raise and lower the idle as necessary. The FICD is used by the ECU to raise the idle to compensate for air conditioning load.

Fig. 48 AAC Valve Operating Conditions:

Refer to chart for AAC operation.