I have a 3 cylinder diesel (universal M30) that hunts in neutral.Under load it runs fine, no blue or black smoke.
Background:
Launched boat and it ran great but within a mile the exhaustriser after the water injection elbow burst sending sea water all over the aftend of the engine. We got a tow back and repaired the exhaust and rinsed awaythe salt water. The next day when relaunching it would not start, I suspectedthe glow plugs wiring. I had to return to work so i hired someone to look intothe glow plugs. When i returned it was stated that the plugs worked fine. Thepower at the last plug was a little low for my liking but the mechanic felt itwas sufficient.
I then started looking into the fuel system. After havingthe injection pump and the injectors rebuilt and the engine still would notfire. I circled back to the glow plugs to discover that they were NOT gettingenough power to get hot. I replaced the switch and the wire and got the engineto run but now i have a problem with it hunting in neutral. I have drained theold fuel out of the tank and replaced the fuel filters. I have switched liftpumps (all rated around 3 to 10 PSI or 15 gal. an hour) with no change. I havelooked at the governor and the idle spring and have visually watched theinjection pump rod that controls the speed and the speed increase starts beforethe rod starts to move and continues until the spring pushes the rod back againstthe governor where the idle should be. I have tried to adjust the springpressure with no change. I inspected the spring and even stretched it a littlebut still no change. The lift pump i have returned to the one that was on itbefore this problem started. I bypassed the fuel tank, then each fuel filterone at a time with no change. I disconnected the fuel return line and checkedit for obstructions. I disconnect the exhaust from the lift muffler to discountany possibility of back pressure from an obstruction there and no change. The fuelinjection pump i had looked at a second time to insure the first shop didnít dosomething wrong, no change.

Short of replacing the governor idle return spring i donít knowwhere else to go with this one.
Any help of where else to look that i am missing?
When left for a day or 2 it can require 2 or 3 cycles ofusing the glow plugs for 1 minute before it starts then it will restart with a30 sec. glow plug actuation. May be unrelated to the hunting issue.

Thanks