Subaru 2002 Impreza Service Manual page 85

CONTROL SYSTEM
Fuel Injection (Fuel System)
Ignition switch ON
a
Fuel pump relay Fuel pump
E: IDLE AIR CONTROL
A certain period of time after ignition switch is turned ON
While cranking the engine
While engine is operating
When engine stops
0
The ECM activates the idle air control solenoid valve to control the bypass air flowing through
the bypass passage in the throttle body depending on signals from the crankshaft position sensor,
engine coolant temperature sensor, pressure sensor and A/C switch so that the proper idle speed
for each engine load is achieved.
0
The idle air control solenoid valve uses a duty-ratio-controlled solenoid which can continuously
vary the opening area of the rotary valve. As the ECM increases the duty ratio, opening of the rotary
valve increases so that the bypass air flow increases, and the engine idling speed becomes higher
as a result.
0
The bypass air control is necessary for:
0
Increasing idling speed when the air conditioning system and/or electrical loads are turned
on.
0
Increasing idling speed during early stage of warm up period.
0
Obtaining dashpot function when the throttle valve is quickly closed.
0
Prevention of engine speed variation during idling.
ON
Operates
ON Operates
ON Operates
OFF Does not operate
Crankshaft position sensor
1 -
Camshaft position sensor
Throttle position sensor
ECM
Engine coolant temperature sensor
Vehicle speed sensor
Ignition switch
N C switch
*Neutral position switch (MT)
*Park/Neutral position switch (AT)
Idle air control
solenoid valve
NF0431
FU-35