Subaru LEGACY 2002 Quick Reference Index page 215

E: IDLE AIR CONTROL
! 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.
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 ro-
tary valve increases so that the bypass air flow increases, and the engine idling speed becomes
higher as a result.
The bypass air control is necessary for:
!
! Increasing idling speed when the air conditioning system and/or electrical loads are turned
on.
! Increasing idling speed during early stage of warm up period.
Obtaining dashpot function when the throttle valve is quickly closed.
!
Prevention of engine speed variation during idling.
!
Intake manifold pressure sensor
Intake air temperature sensor
Crankshaft position sensor
Camshaft position sensor
Throttle position sensor
Engine coolant temperature sensor
Front vehicle speed sensor
Ignition switch
A/C switch
Park/Neutral position switch
F: FUEL PUMP CONTROL
Using the signal from the crankshaft position sensor, the ECM controls operation of the fuel pump
by turning its relay ON or OFF. To improve safety, the fuel pump is stopped if the engine stalls with
the ignition switch ON.
Ignition switch ON
A certain period of time after ignition switch is turned ON
While cranking the engine
While engine is operating
When engine stops
CONTROL SYSTEM
ECM
Fuel pump relay
FU-35
Fuel Injection (Fuel System)
Idle air control solenoid valve
ON
ON
ON
OFF Does not operate
B2H3915A
Fuel pump
Operates
Operates
Operates