Subaru 2002 Impreza Service Manual page 22

AIR LINE
Fuel Injection (Fuel System)
F: IDLE AIR CONTROL SOLENOID VALVE
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The idle air control solenoid valve is located in the throttle body and regulates the amount of in-
take air that flows bypassing the throttle valve into the intake manifold during engine idling. It is
activated by a signal from the ECM in order to maintain the engine idling speed at a target speed.
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The idle air control solenoid valve is a stepping motor type solenoid-actuated valve which con-
sists of coils, a shaft, a permanent magnet, a spring and a housing. The housing is an integral part
of the throttle body.
The stepping motor consists of two paired coils, the coils of each pair being arranged face to
face with a shaft in between.
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The shaft has a screw at the end around which the permanent magnets are arranged.
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As current flows in the form of pulses through the paired coils sequentially while alternating the
polarity, the N and S poles of the permanent magnets around the shaft are repelled by the same
poles of the magnetism generated by the coils. This causes a nut externally fixed to the magnets
and internally engaging with the screw of the shaft to turn.
The shaft then goes upward or downward.
This upward and downward motions of the shaft open or close the valve port, adjusting the
amount of bypass air.
B 2
H
2 0 0 5 B
(1 ) Connector
(2) Permanent magnet
(3) Shaft
(4) Coil
(5) Spring
FU-6