Idle Speed Control System

Fig. 45 Idle-Up Control System:

CIRCUIT OPERATION
The basic idle speed is not controlled by the ECU, but the ECU does control the idle up solenoid. Various sensors transmit signals to the ECU. If the ECU determines an increase in engine idle speed is necessary, it will supply the ground circuit to the idle-up solenoid valve. The solenoid valve opens a passage that allows air to bypass the throttle plate, increasing the idle speed.

Auxiliary Air Regulator Valve:

AIR REGULATOR
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. 56 Idle-Up Solenoid Valve:

IDLE-UP SOLENOID VALVE
When voltage is applied to the solenoid, the windings pulls a plunger, allowing a passage to open so air can pass through.

Fig. 46 Idle-Up Operation:

Refer to the chart for idle up solenoid operating conditions.