Maintenance Manual for J2 Sedan
Electronic Control System
of Engine
234
Trouble phenomenon 8: Normal start-up but unstable idle speed after warmed-up
General trouble position:
1.
Poor quality of fuel; 2. Coolant temperature sensor; 3.Spark plug; 4.Air throttle body and idle
bypass air passage; 5.Intake passage; 6.Idle adjustor; 7.Mechanical part of engine.
General diagnosis procedure:
No.
Operating Steps
Detection
Results
Subsequent Steps
Yes
Repair the intake system
1
Check air filter for blockage and air intake passage for
leakage.
No
Next step
Yes
Next step
2
Check spark plug of each cylinder to observe whether
its model and gap are in compliance with the
specification.
No
Adjust or replace
Yes
Wash related components
3
Dismantle the idle adjustor to check whether there is
carbon deposit in the air throttle body, idle adjustor and
idle bypass air passage.
No
Next step
Yes
Repair circuit or replace
sensor(s)
4
Pull out the connector of coolant temperature sensor
and start the engine to observe whether the idle speed of
engine is unstable during warm-up process.
No
Next step
Yes
Failure of replacement
5
Dismantle the fuel injector and check whether there is
leakage, blockage or too poor flow in the fuel injector
with cleaning analyzer special for fuel injector.
No
Next step
Yes
Change fuel
6
Check fuel condition and observe whether the trouble
phenomenon occurs just after adding the fuel.
No
Next step
Yes
Eliminate mechanical trouble
of engine
7
Check pressure of all the cylinders and observe whether
the pressure difference of each engine cylinders is large.
No
Next step
Yes
Diagnosis help
8
Turn on the ignition switch and check whether the
power supply and earthing are normal.
No
Repair related circuit
