Surging (speed change)

Cause   Correction
If
the condition occurs at idle, the idle speed is set too low for accessories
Adjust
the idle.
   
high
pressure fuel leak
Inspect/correct
leaks in the high pressure lines, fittings, injector sealing washers
or delivery valves.
   
One
or more injectors worn or malfunctioning delivery valve
Replace
delivery valves.
   
Malfunctioning
injection pump
Replace
the pump.