Subaru 2002 Impreza Service Manual page 49

CONTROL SYSTEM
Fuel lniection (Fuel Svstem)
A certain period of time after ignition switch is turned ON
While cranking the engine
While engine is operating
When enaine stoos
E: IDLE AIR CONTROL
ON Operates
ON Operates
ON Operates
OFF Does not operate
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 signalsfrom 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.
Intake air temperature and pressure sensor
Crankshaft position sensor
Camshaft position sensor
Throttle position sensor
Engine coolant temperature sensor
ECM
Ignition switch
A/C switch
Neutral position switch (MT)
ParWNeutral position switch (AT)
Idle air control solenoid valve
NF0033
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.
I
~~~~ ~
Ignition switch ON
I
Fuel pump relay
I
Fuel pump
FU-33