6. Inspect the air fuel ratio in the gasoline engine
When the malfunction affects all cylinders, it is important when troubleshooting to judge whether the A/F is rich or lean. In this inspection, perform an A/F inspection and narrow down the malfunction cause.
7. Inspect the exhaust gas in the diesel engine
When the malfunction affects all the cylinders, inspect the exhaust gas condition and narrow down the malfunction cause to either the three elements.
When white smoke is exhausted
When the temperature is low, a diesel knock sound occurs for a few minutes immediately after the engine starts. When white smoke is exhausted, inspect the after glow function.
When the malfunction is in the after glow function, ignition retard time becomes longer, diesel knocking sound increases, and white smoke is exhausted.
When white smoke is not exhausted
If air is mixed into the fuel, the amount of fuel injection does not become constant. Pressure inequality also causes rough idling, so inspect fuel and compression systems.
8. Narrow down the malfunction based on the abnormal idling speed condition
When idling speed is high or hunting occurs, the intake air volume is considered to be too great.
When idling speed is low, the intake air volume is considered to be too small. Here, narrow down the malfunction cause by checking the idling speed.
Gasoline engine:
When idling speed is high or hunting occurs
(1) ISCV system
• ISCV failure
• ISCV control system failure (ECU, wire harness)
• Water temperature sensor range/performance problem
(2) System of the engine proper
• Throttle body system malfunction (throttle valve does not fully closed)
• Intake system air sucking
When idling speed is low
(1) ISCV system
• ISCV body failure
• ISCV control system failure (ECU, wire harness)
• Water temperature sensor range/performance problem
(2) System of the engine proper
• Throttle body system failure (throttle valve full-closed position failure)
• Clog in intake system
• Engine rotational resistance is increased
9. The causes in diesel engine
• The cause of high idling speed
Narrow down the cause of the idling speed being higher than the specified value
to be in
the accelerator wire or in the injection pump.
Inspection methods
Check whether the injection pump adjusting lever returns to the correct position or
not.
• When it returns
Adjust idling speed
When the malfunction is not eliminated even though the idling speed has been
adjusted,
the malfunction is considered to be in the injection pump.
• When it does not return
Adjust accelerator wire
When the malfunction is not eliminated even though the accelerator wire has
been
adjusted, the malfunction is considered to be the result of accelerator wire drag or
idle-up
device failure.
• The cause of low idling speed
Narrow down the cause of the idling speed being lower than the specified value to be either in the idle-up device, engine proper or in the injection pump.
Inspection methods
As a cause of low idling speed, inspect whether the idle-up devices such as the A/C switch or power steering operates or not.
• Idling speed is low only when the idle-up device is ON
Idle-up device failure
• Idling speed is low when the idle-up device is both ON and OFF
Idle speed poor adjustment Engine rotational resistance is large Injection pump failure
When the injection pump fails, the injection volume in all cylinders equally decreases. As a result, the engine speed becomes slow.