Idling control
| Idling control |
| Idle air control valve (IAC) |
When the accelerator is in the rest position and the throttle butterfly closed, air for the engine is obtained only from the IAC valve.
The control module regulates the degree of opening of the valve in order to maintain idling speed constant. In consequence, the valve opens on engagement of the A/C or on selection of D or R to compensate for the drop in idling speed which would otherwise occur.
The IAC valve, which has a single winding, receives its power supply from the main relay.
A signal from pin 4 of the control module opens the valve by activating the winding (solenoid). A mechanical spring closes the valve .
The signal controls the opening of the IAC valve so that idling speed is always maintained at 800 rpm when the car is stationary.
With a hot engine, the increase in the mass air flow through the valve on engagement of the
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DRIVE position, is about 1.8
grammes per second
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A/C compressor, is about 1.4 grammes per second
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secondary air injection pump, is about 0.9 grammes per second.
The signal is a 100 Hz PWM signal, which at idling speed is: |
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pin 4 - approx. 5-7 V
In the event of a break in the circuit, the opening of the valve is set by the spring so that idling speed will be about 1500 rpm. |
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