Diesel Engine "Surging" or "loping"

[alexpops]

If algae, pour in Biobor to kill & try polishing the fuel in the tank. Look at Boat videos for DIY polishing systems (basically a 12v fuel pump/filter/lines) & run that stirring up the tank.

Here's one option:

 

[RayIN]

My diesel engine has developed a problem with "surging" or "loping." The engine speed changes dramatically repeatedly below 2200 RPM It will jump from 800 to 1500 down to 1200 up to 1800 and so on. Sometimes it will drop below idle speed and shut off the engine.

This speeding up-slowing down is constant. The only way to stop the cycle is bring engine speed up to operating RPM=2200. Even then the speed varies a little bit, in the 2000-2200 range.

This started the last time I used it (2 days ago). Engine has less than 100 hours.

Ideas of why - and how to fix it?

That is the tell-tale sign of air getting into the fuel system.