Mitsubishi Lancer Evolution VI User Manual

MPI – Troubleshooting
13-25
INSPECTION PROCEDURE 8
Unstable idling (Rough idling, hunting)
Probable cause
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.
D Malfunction of the ignition system
D Malfunction of air-fuel ratio control system
D Malfunction of the ISC servo system
D Poor compression
D Drawing air into exhaust system
D Secondary air backflow to the intake system
Were the battery terminals disconnected recently?
Yes
After warming-up, let the engine run at idling for about 10 minutes.
No
MUT-II Self-Diag code
Are diagnosis codes displayed?
Yes
Refer to P.13-8, INSPECTION CHART FOR DIAGNOSIS CODES.
No
Does idling speed fluctuate excessively?
Yes
Check if hunting occurs.
(Refer to P.13-48, INSPECTION PROCEDURE 40.)
No
Check the ISC servo for operation sound.
NG
Check the ISC servo system.
(Refer to P.13-44, INSPECTION PROCEDURE 33.)
OK
Check the injector for operation.
NG
Check the injector system. (Refer to P.13-15, INSPECTION PRO-
CEDURE FOR DIAGNOSIS CODE 41.)
OK
MUT-II: Check if idling speed is unstable.
(Refer to P.13-49, INSPECTION PROCEDURE 41.)
OK
Check the ignition timing.
(Refer to GROUP 11 – Engine Adjustment.)*
NG
Check that the crank angle sensor and the timing belt cover are
installed properly.
OK
Check the following items.
D Check the ignition coil, spark plugs, spark plug cables.
D Check the secondary air supply system. (Ensure that there is no back flow of secondary air into the intake system.)
D Check the compression pressure.
D Check if foreign materials (water, alcohol, etc.) got into fuel.
NOTE
*: Refer to Workshop Manual for LANCER EVOLUTION-IV and EVOLUTION-V (Pub. No. S9806CNCP9).

Mitsubishi Lancer Evolution VI Specifications

General

Brand	Mitsubishi
Model	Lancer Evolution VI
Category	Automobile Parts
Language	English