250 OX66 EFI Erratic RPM's

Ran boat Monday and put 40 or so miles on it with no problems. Tuesday morning started engines and Starboard motor was idling erratic during warm up. After warm up it would range from 300-800 rpm’s and eventually shut off. If I bump it into high idle for a couple minutes it will clear up and run fine. No problems running under way rpm’s hold consistent with port motor. I can run 10 miles or so and let sit 30 min. and it will do it again. Couple min. of high idle and it corrects it self. Pulled plugs this am after warm up to do compression check and all very wet with fuel. It is like it is flooding motor out. Could it be stuck in warm up mode?

Things checked:
plugs replace less than 10 hrs ago

lift pumps- detached from block. pumped them up with bulb, and none leaking

Oxygen sensor- replace couple months ago, and checked tube to be clear

compression check all cylinders even and good

VST tank drained- no visible contamination

racor checked and drained no water there

sounds like a possible dirty injector, but have u checked the 0-2 sensor since the problem started?


Checked oxygen sensor tube to see if it was blocked, and no carbon build up there. I don’t have meter with me to check 0hms though. It was replaced couple months ago.