Engine mechanism - Engine assembly
CO HC Trouble occurrence Possible causes
28
Normal High Unstable idle speed
Low High Unstable idle speed
(HC readings not stable)
High High Unstable idle speed
(black smoke emission)
1. Ignition system malfunction
Ignition timing incorrect
Spark plug too dirty, short circuit or clearance
incorrect
2. Valve clearance incorrect
3. Air inlet and exhaust valve leaky
4. Cylinder leaky
1. Vacuum leak:
PCV hose
Intake manifold
Throttle body
Idle speed stepping motor
Vacuum booster and pipelines
2. Fire caused by too thin mixing ratio
1. Air filter core blocked
2. PCV valve blocked
3. EFI system malfunction
Fuel pressure regulator malfunction
Water temperature sensor malfunction
Intake pressure sensor malfunction
ECU malfunction
Injection nozzle malfunction
Throttle position sensor malfunction
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