73

7. 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 152

Rough 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

74

8. 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.

75

10. Engine overheat (Table 6)

Table 6

Item

Symptom Troubleshooting

Repair or replace

Bad radiator hose

Replace

Bad radiator tube strap

Supplement welding, otherwise
replace it

Bad cylinder gasket

Replace

Cracky cylinder block

Remedy with infiltration technology
or replace it

Poor water pump seal

Replace the seal
Replace the anti-freeze liquid
Replace the thermostat

Broken weld

Supplement welding

Corrosion result in pin hole

Fill the pinhole with clear coat,
otherwise replace it
Repair and dredge
Improve the ventilation
Repair or replace the water pump
Troubleshooting, replace the motor if
it is damaged

Replace
Repair and dredge
Repair or replace the oil pan if there
is oil leakage, refill the oil if it is not
supplemented in time

Cause

Bad radiator cover

Clogged cooling tube

Poor ventilation

Water

leakage

Anti-freeze liquid not replaced

Bad thermostat

Radiator is

faulty

Water

leakage

Insufficient

coolant

Faulty fan voltage

Disabled radiator temperature control

switch

Water jacket is clogged because of too much scale

Insufficient engine oil (oil leakage or delayed filling)

Poor

cooling

Poor Fan

Faulty water pump

76

11.  General engine fault symptom and faulty area (Table 7)

Table 7

Unable to explode initially

Una

ble

 to e

xplode

 c

omple

te

ly

Di

ffi

cul

t for col

d st

art

Di

ffi

cul

t for hot

 st

art

No f

ast ilde

Low idle

 spe

ed

High idle

 spe

ed

Rough ildling

Id

le

 hunting

At

 urgent

 accel

erat

io

n

When t

he accel

erat

or pedal

 is

 rel

easec

Dur

ing idling

P

oor accel

erat

io

n

Hunting during driving

Insuffi

ci

ent

 power

Knock

Intake abosolute pressure

sensor

c c c c c c c

c c

Water temperature sensor

c c c c

c c

c

c c

c

Revolution speed sensor

c

Throttle valve position

sensor

c c c

c c c c c

Vehicle speed sensor

c

Fuel pump system

c c

c

c c

c

Fuel pressure regulator

c c c c c

c

c c c c

Fuel filter and pipeline

c c

c

c c c c

Injector

c c c c c

c

c c c

Starter signal

c c

Ignition coil

c

c

c

Spark plug

c c c c

c

c c

c

High pressure cable

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 power supply circuit

c

Ignition swtich

c

Main relay

c

Fuel pump relay

c

Poor driving

Difficult to start     Poor idling                Engine off

Power
supply

system

Control

system

Fuel

system

Ignition

system

Intake

air

system

Suspect
Area

Symptom