1999 150 Optimax Won't Idle & Has Excessive oil

[twin200merc]

My Dad's 1999 150 Optimax idle goes really low, comes back up, goes really low, comes back up and then goes so low it dies... Any ideas? It has a new water pump, new Optima Battery, spark plugs less than 1 year old, and new water/fuel seperator.

This is on a ski boat so it spends 90% of its time at idle and very rarely sees RPMs over 3,000, but they do occationally barefoot and that is at almost WOT.

** 2nd issue, there appears to be oil inside the intake... when I open the throttle body I can see a little bit of oil sitting at the bottom. There is also some oil in the lower cowel that will drip into the engine well if trimmed up for a period of time. I have no idea why...

Thanks for the help guys! I really appriciate it!

Mike

[Revolution141]

Oil in intake is normal. Not sure why it's in cowl but I suggest checking all the tiny oil lines that go to the various bearings on the motor. These are only push on and one may have come off. Regarding the idle problem I had the same symptoms with my 300xs after about 2hrs. Took me months to work it out but it ended up being a pin hole air leak in air hose from compressor to fuel/air rail. Check this hose and replace if any air is escaping. Otherwise just check for general air leaking around rails and compressor. These motors don't run well once air/ fuel pressures are indifferent. A merc dealer will be able to hook up gauges to fuel rails to know for sure if it's a air leak problem.

[ChrisCarsonMarine]

Try a power tune treatment through the compressor to clean/free the air injectors,I'd this doesnt help consider reeds,these motors suffer from broken/chipped reeds often,chris

[twin200merc]

How do I do a power tune? Where do I get that?

Thanks,
Mike

[hometown45]

Another thing to check is the cap on the engine oil tank, they are notorious for coming loose after someone has OVER-tightened them.