Page 985 - Workshop Manual - Tunland (2017)

DIAGNOSTICS - ENGINE CONTROL SYSTEM 04-299

UNSTABLE IDLING (FLUCTUATED) 04

Fault phenomenon Diagnosis logic Diagnosis logic
• Injector
• Intake system • Leakage in the intake
• Fuel system system
• Wrong mixture ratios • Air fuel ratio
• Carbon decomposition of • Electronic throttle valve
Unstable idling (fluctuated)
cylinder valve and inlet • Oil leakage in the injector
channel • Too low of the compression
• Air fuel ratio pressure
• Electronic throttle valve • Fuel pressure
• ECM

CAUTION

When the motor idling runs, if the mixture gas distribution disorders, intake system
leaks or some cylinder doesn't work due to the ignition system failure, it will cause
the default of no idle, too high idle speed, unstable idle or poor idle and other defaults.

Diagnosis Procedure

1 . Possible reasons

(a) Ignition switch: OFF.
(b) Connect the diagnosis tool with the fault diagnosis connector (16 pins) on the lower
left of the dashboard.
(c) Ignition switch: ON, and start the diagnostic tool.
(d) Read the motor data shown on the diagnostic tool.

Check whether the data flow is normal or not.
YES>To step 2.

No >Maintenance related faults.

2 . Perform visual and external check
(a) Observe the rotation status and shaking degree of the motor.
(b) At the same time, observe the swing range of the engine tachometer indicator, and
check whether it deviates from the idle target value.
(c) Observe whether it is normal idle jitter or load idle jitter. (Turn on the air conditioner,
light, hanging gear and turn the steering wheel etc.)
(d) Whether the external parts of the motor are normal or not; whether the wire connector
looses or not.
(e) Whether it has the four phenomena of leakage of fuel, water, gas and electricity.
(f) Whether the exhaust pipe has the phenomena of “chug, chug” (indicating poor
combustion), black smoke, raw gasoline smell and other abnormal phenomenon.

Is the inspection result normal?
YES>To step 3.

No > Exclude the problem and confirm that the phenomenon no longer exists.