Page 76 of 392
69j. Poor intake and exhaust valve seal, failed piston ring, low compression pressure;
h. Too many carbon deposit in spark plug and combustion chamber;
k. Water temperature switch and thermostat fault;
l. Aging of Oxygon sensor;
m. Incorrect ignition timing;
n. Check valve fault.
Figure 149Engine is difficult to start
Check whether the air cleaner is clogged Clogged
Troubleshooting
OK
Check the idle control valve NG
Repair or replace
OK
Check the fuel pressure Excessivly low
Service the electric fuel pump,
fuel filter and fuel pressure regulator
OK
Check the vacuum pressure sensor NG
Replace
OK
Check the water temperature sensor and intake air temperature sensor NG
Replace
OK
Check the start switch signal No
Service the start signal wire
OK
Check the ignition timing Misaligned
Adjust
OK
Check the cylinder pressure NG
Disassemble the engine
OK
Replace the ECU to retry
Page 77 of 392

70(3) Diagnosis procedure for insufficient engine power (Figure 150)
2. Poor deceleration
(1) Symptom
Idling is normal, but the engine is frequently turned off upon sudden release of the accelerator pedal
during driving.
(2) Causes and Troubleshooting:
a. Throttle position sensor is damaged and shall be replaced;
b. Initial idling is not properly adjusted or automatic idle control is wrong, fuel cut RPM is too low,
ECU fault, repair or replace them.Insufficient power
Insufficient
Check whether throttle valve can be fully open Unable to be fully open
Adjust
OK
Check whether the air cleaner is clogged Clogged
Clean or replace
OK
Check the throttle valve position sensor for failure Abnormal
Repair or replace
OK
Check the water temperature switch and thermostat NG
Replace
OK
Check the vacuum pressure sensor for failure NG
Replace
OK
Check the fuel pressure Excessively low or high
Service the electric fuel pump,
fuel filter and fuel pressure regulator
OK
Check the oxygen sensor Incorrect
Replace
OK
Check the injector Incorrect
Replace
OK
Replace the spark plug, ignition coil and high voltage wire
OK
Disassemble the engineFigure 150
Page 79 of 392

724. Big fuel consumption
(1) Symptom:
Engine power is ok, but the fuel consumption is big, exhaust pipe discharges black smoke.
(2) Causes and Troubleshooting:
a. When idling, idle speed is high and shall be adjusted;
b. Water temperature sensor fault, service or replace it;
c. Water temperature switch and thermostat fault, repair or replace it;
d. Oxygen sensor fault, repair or replace it;
e. Fuel pressure is big and shall be adjusted;
f. Injector fault (fuel leakage), repair or replace it;
g. Throttle position sensor fault, repair or replace it;
h. Fuel pressure regulator is damaged and shall be replaced;
i. Intake pressure temperature sensor fault, repair or replace it.
5. Unstable idle, liable to be turned off
(1) Symptom:
Engine starts normally, but the idle is unstable regardless of cold or hot status, idle speed is too low and
the engine is liable to be turned off.
(2) Causes and Troubleshooting
a. Poor idle control valve operation, repair or replace it;
b. Low idle speed and faulty or improperly adjusted idle control valve, troubleshoot it;
c. Water temperature sensor fault, repair or replace it;
d. Poor intake system seal, need to be repaired;
e. High voltage spark is too weak, spark plug carbon deposit or electrode clearance is too small, need
to be repaired, cleared and adjusted;
f. Pressure sensor fault, repair or replace it;
g. The compression pressure in the cylinder is too low, need to be serviced;
h. Fuel line pressure is too low, needed to be serviced;
i. Air cleaner is clogged, clean or replace it;
j. Poor injector atomization, fuel leakage, block or big injection variation, need to be repaired;
(3) Diagnosis procedure (Figure 152)
6. Unstable idle at cold status, liable to be turned off
(1) Symptom
During the cold start, idle is unstable and engine is liable to be turned off, the normal idle is recovered
after warming of the engine.
(2) Causes and Troubleshooting
a. Water temperature sensor fault, repair or replace it;
b. idle control valve fault, repair or replace it.
Page 80 of 392

737. Unstable idle or engine shut off at hot status
(1) Symptom
Idle speed is normal during the cold start and becomes unstable at hot status, idle speed is too
low or engine is shut off.
(2) Causes and Troubleshooting
a. Idle is adjusted too low, adjust it to normal condition;
b. Water temperature sensor fault, repair or replace it;
c. Poor injector operation or big injection variation, repair or replace it;
d. Poor water temperature switch and thermostat operation, repair or replace it;
e. Check valve is damaged and needs to be replaced.
Figure 152Rough ildling, easy for engine shut off
Check whethe the air tightness of the intake system is good Poor
Troubleshooting
OK
Check idle control valve for operation Inoperative
Disassemble or replace
Operative
Reset the initial idle speed
Check the spark plug Poor
Adjust the clearance or replace
OK
Check the fuel pressure NG
Check the electric pump, fuel
pressure regulator and fuel filter
OK
Check the injector NG
Replace
OK
Check the pressure sensor NG
Replace
OK
Check the cylinder compression pressure NG
Disassemble the engine
OK
Check and adjust the valve clearance
Page 81 of 392

748. Idle speed too high at hot status
(1) Symptom
The engine runs at fast idle during cold start and remains fast idle at hot status, leading to excessively fast
idle.
(2) Causes and Troubleshooting
a. The initial idle value is not properly adjusted,
b. High system fuel pipeline pressure, need to be adjusted;
c. Water temperature sensor fault, repair or replace it;
d. Water temperature switch and thermostat fault, repair or replace it;
e. Idle control valve fault, repair or replace it;
f. Throttle is binding and not tightly closed, repair or replace it;
g. Fuel evaporation control valve is always open, repair or replace it;
h. Speed sensor fault, repair or replace it.
9. Idle fluctuation
(1) Symptom
when idling, the engine speed fluctuates.
(2) Causes and Troubleshooting
a. Intake pressure temperature sensor fault, repair or replace it;
b. Check valve is damaged and needs to be replaced;
c. Water temperature sensor , water temperature switch and thermostat is poorly coordinated, repair,
adjust and troubleshoot them;
d. Oxygen sensor fault, need to be replaced;
e. Spark plug poor connection, repair or replace it;
f. Idle control valve and its control circuit fault, repair or replace it;
g. Idle switch is not closed, need to be repaired.
Page 83 of 392

7611. General engine fault symptom and faulty area (Table 7)
Table 7
Unable to explode initially
Unable to explode completely
Difficult for cold start
Difficult for hot start
No fast ilde
Low idle speed
High idle speed
Rough ildling
Idle hunting
At urgent acceleration
When the accelerator pedal is releasec
During idling
Poor acceleration
Hunting during driving
Insufficient power
KnockInta ke a bosolute pre ssure
se nsor
c c c c c c c c c
Water temperature sensor c c c c c c c c c c
Re volution spee d se nsor
c
Throttle valve position
se nsor
c c c c c c c c
Vehicle speed sensor
c
Fuel pump system
c c c c c c
Fue l pre ssure regulator
c c c c c c c c c c
Fue l filte r a nd pipe line
c c c c c c c
Injector
c c c c c c c c c
Sta rte r signal
c c
Ignition c oil
c c c
Spark plug
c c c c c c c c
High pre ssure ca ble
c c
Ignition timing
c c c c c c c
Igniter in the ECU
c c c c
Throttle valve
c c c c c
Throttle valve body c c c
Air leakage in the intake
air system c c c c c c c c
Air valve
c c c c c
ECU powe r supply circuit
c
Ignition swtich
c
Ma in re la y
c
Fuel pump re lay cPoor driving Difficult to start Poor idling Engine off
Power
supply
system Control
system
Fuel
system
Ignitio n
system
Intake
air
systemSuspect
AreaSymptom