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How To Repair When The Idling Speed Of The Engine Is Unstable?

Phenomenon of Malfunction

whether in the cold or heat conditions, the idling speed of the diesel engine is not stable. The body shakes seriously with the speed sometimes high and sometimes low, and even cannot maintain the normal operation and turn off.

Judgment of Malfunction

1、The idling speed is too low;
2、There is air in the fuel system;
3、The oil injection pump is not working properly;
4、The oil injection is not at the right time;
5、The oil injector is clogged or not working properly;
6、The engine support pads loose or broken.


1、 Start the engine and observe the tachometer. If the speed value indicated is low and accompanied by the shake of the body, check whether the idle speed limit screw is loose and disordered. If not, add a litter fuel to raise the speed of the engine to the specified idle speed. If the engine can operate stably and evenly without any shake, it indicates that the failure is the improper adjustment of the idle speed.
2、When the engine is idling, observe whether the high-pressure pipe connection has leakage. If it leaks, the cylinder is of poor operation, which causes the unstable idle speed. Then the high-pressure pipe shall be repaired or replaced.
3、When the engine is idling, loosen the air release screw to observe the oil outlet situation. If there are a lot of bubbles emitting from the air release screw hole, it indicates that there is air in the fuel. Check whether there is leakage at all the connections between the fuel pump and the fuel tank and exclude it if it leaks.
4、If the idle speed is still unstable, respectively touch the high-pressure pipe of each cylinder when it idles by hand and feel the strength of the oil injection pulse of each cylinder. If certain cylinder fuel injection pulse is weak, further cut off the fuel artificially for the cylinder. If the speed of the engine does not have much change when it is cut off, it indicates that the cylinder is of poor operation and the injector of the cylinder shall be removed for examination.
5、When it is in urgent acceleration, if the engine has an obvious metal percussion, it indicates that the injection may be too early. If the engine speed increases slowly after retardation, it indicates that the injection is too late. If the injection is not in the right time, it shall be re-adjusted.
6、If the above tests are normal, detect the cylinder pressure of the engine. The cylinder pressure difference shall not be exceeding the specified value.

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