5 

 

No. 003 Over idle speed when warm-up 

Malfunction Cause 

Solution 

Improper ignition time 

Adjust ignition time 

Incorrect fuel pressure 

Check fuel pressure, whether the value is 265~304kPa. If it is 
abnormal, shall check fuel pump and pressure controller, as well as 
the balance fuel injection volume of each injector. 

Throttle cable or inner 
damper fails to return origin 
position 

If throttle cable or inner damper fails to return origin position, sc. 
opening degree remains, shall check throttle cable and throttle. 

Idle speed control valve or 
stepping motor stuck 

Check idle controller, whether there is over carbonization. Implement 
clean and self-adaption value adjust when necessary. 

Intake system leak 

Check intake system, whether it is leaking. Maintain or replace when 
necessary. 

The sensitive resistance 
temperature coefficient of 
water temperature sensor 
indicates inaccurately 

Check water temperature sensor, at each temperature, whether the 
operation resistance is in regulated range. For example, at 20 ± 1 

℃

 (temperature tolerance), the resistance shall be 2.27~2.73kΩ. 

℃
Replace when necessary. 

Exhaust gas oxygen sensor 
malfunction 

Check heater resistance of heated oxygen sensor (UAES 1~6Ω, 
Delphi 12Ω, Polarsun 13.2±10%) , heater voltage (12V) and signal 
voltage (0.1~0.9V), whether they are normal.   
Check oxygen sensor, whether it is polluted or poisoned. When 
oxygen senor outputs low voltage or signal error, then ECU will send 
thick injection order, otherwise, replace the sensor. 

A/C control signal error 

Check A/C controlling system, whether it is normal.   
Check pressure switch current, whether it is normal.   
Check AC system pressure, whether it is normal. 

Idle speed raised 
when warm-up 

ECU inner data unmatching 

Check ECU, whether it is damaged. Replace ECU assembly when 
necessary. 

 

 
 

 

 

6 

 

 

Over idle speed when warm-up 

Water temperature sensor malfunction 

Oxygen sensor malfunction 

Intake system leaking 

Idle speed control valve or stepping motor stuck 

Incorrect fuel pressure 

A/C control signal error 

Improper ignition time (too early) 

Throttle cable or damper malfunction 

ECU inner malfunction 

Normal 

Normal 

Normal 

Normal 

Normal 

Normal 

Normal 

Normal 

Abnormal 

Abnormal 

Abnormal 

Abnormal 

Abnormal 

Stuck 

Abnormal 

Abnormal 

Abnormal 

Replace 

Replace 

Check 

Check 

Adjust 

Check 

Replace 

Clean or replace 

Maintain 

 
 

 

 

7 

 

No. 004 Idle speed fluctuation   

Malfunction Cause 

Solution 

Throttle is stuck and 

dirty 

Clean and check throttle sealing condition. 

Ignition maladjustment 

Check spark plug, whether it is dirty, cracked or tracking; 
Check wire of each cylinder, whether they are ageing, tracking, short or open circuit;
Check ignition timing, whether it is maladjustment. (ignition timing shall position at 
10~12° before top dead center when idling. Adjust ignition timing advance angle if 
necessary, when accelerating, the angle shall increase 20~30°) 

Voltage unstable 

Check battery voltage, whether the value is 12~14.5V; 
Check generator, whether it operates normally; 
Check body earth lead, whether it is fastened. 

Sensor and executive 

unit malfunction 

Check cooling temperature sensor, whether the resistance is according with the 
standard in different temperatures. 
Check intake temperature sensor, and replace it when necessary. 
Check idle speed control valve or stepping motor, whether it is stuck or damaged, 
clean or replace it when necessary. 
Check throttle position sensor, whether the bolts are over raised, and adjust them 
when necessary. 
Check oxygen sensor, whether it waves between 0.1V and 0.9V.   
If injector sealing leaking, then replace injector assembly. 
If spark plug operates poorly, then replace the plug. 

Exhaust system 

malfunction 

Check canister, whether it is polluted and blocked. 
Check exhaust pipe, whether it is deformed and damaged. 
Check 3-way catalytic converter, whether it is damaged or blocked. 

Poor tachometer 

sensitivity 

Check instrument connector, whether it is poor contact. Fix it again when necessary. 
If it conducts normally, then replace the instrument panel. 

ECU malfunction 

Test the voltage between each 2 terminals of ECU, whether the value is in normal 
range. 
Check the connecting condition between ECU and wire. 
Load data stream according to origin data.     

 

Engine mechanical 

malfunction 

Check the pressure difference between each cylinder, whether they are over normal 
range.  
Check the sealing condition of each cylinder. 

 
 

 

 

8 

 

Idle speed fluctuation 

Throttle is stuck and dirty 

Ignition maladjustment 

Exhaust system malfunction 

Voltage unstable 

Sensor and executive unit malfunction 

ECU malfunction 

Engine mechanical malfunction 

Normal 

Normal 

Normal 

Normal 

Normal 

Normal 

Abnormal 

Abnormal 

Abnormal 

Abnormal 

Abnormal 

Abnormal 

Stuck, dirty 

Clean 

Adjust 

Check or replace 

Check 

Replace 

Check or replace 

Replace