Mitsubishi 3000GT Service Manual page 257

IDLE AIR CONTROL MOTOR (STEPPER MOTOR TYPE)
OPERATION
The intake air volume during idling is controlled by opening or closing the servo valve provided in
l
the air path that bypasses the throttle valve.
The servo valve is opened or closed by operating the stepper motor in the speed control servo
l
in normal or reverse direction.
The battery power is supplied to the stepper motor through the MFI relay. As the engine control
l
module turns on power transistors in the module one after another, the stepper motor coil is energized
and the motor rotates in normal or reverse direction.
TROUBLESHOOTING HINTS
Hint 1: If the stepper motor step increases to 100 to 120 steps or decreases to 0 step, faulty stepper
motor or open circuit in the harness is suspected.
Hint 2: If the idle air controll motor harness and individual part checked good but the stepper motor
steps are out of specification, the following faults are suspected.
(1) Poorly adjusted reference idle speed
(2) Deposit on the throttle valve
(3) Air leaking into the intake manifold through gasket gap
(4) Loose EGR valve seat
(5) Poor combustion in the cylinder (faulty ignition plug, ignition coil, injector, low compression pres-
sure, etc.)
MULTIPORT On-Vehicle Inspection of MFI
FUEL INJECTION - Components
Engine control module connector
TSB Revision
6
1 "3
A Harness side