Idle Up Control Valve: Description and Operation

Fig. 7 Idle-up compensator system:

Idle speed compensation is provided for varying engine loads by a vacuum operated idle-up compensator which is controlled by a Three-Way Switching Valve (TWSV), Fig. 7. The ECM sends electrical signals to the TWSV in order to control idle-up compensator operation. When an electrical signal is transmitted to the TWSV, the inner diaphragm of the valve opens and allows manifold vacuum to be applied to the compensator. Manifold vacuum is applied to the compensator diaphragm which in turn operates an adjusting rod and screw assembly. The rod and screw move down in response to vacuum applied to the diaphragm, opening the throttle to compensate for increased engine loads.



Manual Transmission
On models with manual transmission, the idle-up compensator is used to raise idle speed to compensate for the following conditions:
When electrical accessories are operated, the ECM energizes the TWSV to stabilize engine idle speed. When the electrical load is removed, the TWSV is switched off and idle speed is controlled by the throttle stop screw.
The TWSV is energized for approximately 5 seconds after a warm engine is started.
The TWSV is energized when oxygen sensor temperature is low and the sensor is not satisfactorily activated.
Automatic Transmission
On models with automatic transmission, the idle-up compensator system is activated when the transmission selector is placed in any drive range and road speed is below 15 mph. In addition, the system is activated when oxygen sensor temperature is low and the sensor is not satisfactorily activated.
Refer to ``Emission Control Systems'' section for description of bowl vent, fuel cut and pulse air or secondary air control system operation.