Mitsubishi MOTORS Space Runner 1999 Workshop Manual Supplement page 508

INSPECTION PROCEDURE 8
Unstable idling (Rough idling, hunting)
In cases as the above, the cause is probably that the ignition system, air/fuel mixture,
idle speed control (ISC) or compression pressure is defective.
Because the range of possible causes is broad, inspection is narrowed down to
simple items.
Were the battery terminals disconnected?
MUT-II Self-Diag code
Are diagnosis codes displayed?
Does idling speed fluctuate excessively?
Check the ISC servo for operation sound. (Refer to P.13B-75.)
Check the injector for operation sound.
MUT-II Data list
14 Throttle position sensor (Refer to P.13B-48.)
MUT-II Data list
13 Intake air temperature sensor (Refer to P.13B-48.)
MUT-II Data list
21 Engine coolant temperature sensor (Refer to P.13B-49.)
MUT-II Actuator test
08 Purge control solenoid valve (Refer to P.13B-52.)
MUT-II Actuator test
10 EGR control solenoid valve (Refer to P.13B-52.)
MUT-II Data list
59 Oxygen sensor (rear) (Refer to P.13B-51.)
Transmission: 2nd gear
Driving with throttle widely open
OK: 600 – 1,000 mV
MUT-II Data list
11 Oxygen sensor (front)
OK: 600 – 1,000 mV during sudden racing
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MPI –
No
No
No
OK
OK
OK
OK
OK
OK
OK
OK
OK
Troubleshooting
Probable cause
Malfunction of the ignition system
Malfunction of air-fuel ratio control system
Malfunction of the ISC system
Malfunction of the purge control solenoid valve system
Malfunction of the EGR solenoid valve system
Poor compression
Drawing air into exhaust system
Yes
After warming-up, let the engine run at idling for 10 minutes.
Yes
Refer to P.13B-9, INSPECTION CHART FOR DIAGNOSIS
CODES.
Yes
Check the throttle body. (Refer to P.13B-65.)
Check trouble symptom.
Inspect the intake of air into the air intake system.
Broken intake manifold gasket
Broken air intake hose
Broken vacuum hose
Positive crankcase ventilation valve does not operate.
NG
Check the ISC servo system.
(Refer to P.13B-46, INSPECTION PROCEDURE 32.)
NG
Check the injector system. (Refer to P.13B-17, INSPECTION PRO-
CEDURE FOR DIAGNOSIS CODE 41.)
NG
Check the throttle position sensor system. (Refer to P.13B-12,
INSPECTION PROCEDURE FOR DIAGNOSIS CODE 14.)
NG
Check the intake air temperature sensor system. (Refer to
P.13B-11, INSPECTION PROCEDURE FOR DIAGNOSIS CODE
13.)
NG
Check the engine coolant temperature sensor system.
(Refer to P.13B-13, INSPECTION PROCEDURE FOR DIAGNO-
SIS CODE 21.)
NG
Check the purge control solenoid valve system.
(Refer to P.13B-46, INSPECTION PROCEDURE 33.)
NG
Check the EGR control solenoid valve system.
(Refer to P.13B-47, INSPECTION PROCEDURE 34.)
NG
Check the oxygen sensor (rear) system. (Refer to P.13B-19, IN-
SPECTION PROCEDURE FOR DIAGNOSIS CODE 59.)
NG
Check the oxygen sensor (front) system. (Refer to P.13B-10, IN-
SPECTION PROCEDURE FOR DIAGNOSIS CODE 11.)
13B-27
NG