very high idle

[Trevor]

By-Pass Air Control Solenoid Valve
Cleaning, setting and Testing.

Description.

The By-Pass Air Control Solenoid Valve, or Idle Air Control Valve, allows the Engine Control Unit/Computer, to adjust the inlet of air after the throttles, in order to control idle speed. One obvious function is to increase the airflow when the air conditioning system imposes an extra load on the engine.

The unit comprises a rotary solenoid valve, biased towards a central rest position, by means of a permanent magnet. A double wound coil provides reversing open closed operation from a mean rest position, at which point the valve is half open. This arrangement provides two way variable control, dependent on the applied voltage.

Three electrical connections are involved. The centre pin on the connector is common to both windings and is energised positive. The remaining two connections provide for open and close operation of the valve.

Cleaning and Adjusting.

Cleaning is best achieved by removing the solenoid coil by undoing the two attachment screws, which pass through slotted holes so as to provide a degree of adjustment. Make a scratch mark so that the original position can be retained after reassembly. Magnetic force will be apparent as the solenoid coil is separated from main body.

The armature which rotates in ball races, when moved by hand should rotate open closed, with virtually no resistance. The valve should be cleaned of foreign matter using a suitable solvent/lubricant so that it is completely free to move.

After reassembly the valve should rest in a position, half open and half shut when set to the original mark. If there is a large discrepancy, this may indicate that the setting has been tampered with at some time and it should be reset.

Testing.

The solenoid resistance should measure 9 ohms, each side of the common connection, i.e. 18 ohms overall, a small tolerance being acceptable.

With positive to the common connection, 8 volts DC applied separately in turn to the two remaining connections, should fully open and close the valve from rest. Return to the rest position should occur, reliably without hesitation. In the event that 12 volts must be used, this will suffice for intermittent testing, but the extra torque available must be appreciated,

If a variable voltage source is available, continuous opening closing according to the applied voltage can be reproduced. However this test is in no way a necessity.