Mitsubishi 1989-1993 GALANT Service Manual page 441

FUEL SYSTEM <DOHC> -
OPERATION
The amount of air taken in during idling is
l
regulated by the opening and closing of the
servo valve located in the air passage that
bypasses the throttle valve.
The servo valve is opened or closed by the
l
activation of the stepper motor (incorporated
within the idle air control motor) in the forward
or reverse direction.
TROUBLESHOOTING HINTS
Hint 1: If the number of stepper motor steps
increases to IOO- 120 steps or decreases
to 0 step, the cause may be presumed to
be a malfunction of the stepper motor or
damaged or disconnected wiring of the
harness.
Hint 2: If the number of stepper motor steps
deviates from the standard value even
though the results of the checking of the
harness of the idle air control motor and of
the comoonent itself indicate no abnormal
condition, the cause may be presumed to
be one of the following.
INSPECTION
Using Scan tool
Function
Data reading 45
NOTE
When the vehicle is new (driven approximately 500 km (300 miles) or less) the number of steps may be about
30 steps greater than the standard value indicated above.
Data display Check conditions
Stepper . Engine coolant tempera-
motor steps ture:
. Lights, electrical cooling
fan and accessories: OFF
. Transaxle: neutral
. Closed throttle switch: ON
(The compressor clutch
should be activated when
the air conditioning switch
is switched ON.)
Using Oscilloscope
(1) Connect the probe to each oscilloscope pick-up point as
shown in the circuit diagram.
(2) Start the engine.
speed increases to operate the idle air control. Check the
instantaneous waveform.
NOTE
Keep in mind that the waveform can be observed only
when idle air control is in operation.
Battery power supply is supplied, by way of the
l
stepper motor. The engine control module
switches ON the power transistors (located
within the engine control module) in sequential
order, and, when current flows to the stepper
motor coil, the stepper motor is activated in the
forward or reverse direction.
idling speed.
(2) Deposits adhered to the throttle valve.
(3) Leakage of air into the intake manifold
from a gasket gap, etc.
valve seat.
(5) Incomplete
cylinder.
(Malfunction of the spark plugs, the
ignition coil, the iniectors, the com-
Load conditions
. Air conditioning
switch: OFF
switch: ON
13-299
combustion within the
Standard value
<Non-Turbo>
<Non-Turbo>