Merc 350 Mag MPI jerking/popping

Just wanted to start off by saying this is my first post on this website but I have been following this forum for a couple of years now, ever since I was looking to buy my first boat.

I have a 2002 Sanger DLX with a merc 350 mag mpi direct drive engine. I had this problem for 3 seasons now but nerver figured out what the problem could be. When I run the boat on idle, sometimes the engine would jerk, kind of making a popping sound. It will only do it while in idle.

Another thing, and I don't know if the problem is related, but when I have the boat running at any steady speed, the idle will sometimes fluctuate up and down without touching the throttle.


Any thoughts?


Thanks!

have you had a scan done? This could be a million things

No scan done yet. I am planning on bringing it in to a mechanic this weekend. I was just wondering if someone had a similar problem before.

Sounds like lean pops but seems unclear why it would only happen at idle? I would suspect fuel pump/fuel delivery issue...

Sounds like lean pops but seems unclear why it would only happen at idle? I would suspect fuel pump/fuel delivery issue...

I was thinking that but makes very little sense to have that happen only at idle. MAP sensor would be the first thing that comes to my mind or IAC although this problem is usually backwards. What rpm are you at at idle? This is prob a simple fix of getting a scan and going from there.

I was also thinking of some kind of fuel issue, but since its only doing it at idle.... Thats why I mentionned when I run the boat at any speed, the rpm would go up and down slightly without touching the throttle. I thought maybe the problems were linked. But ya like you said I will go have it scanned and see what comes out. I run idle at around 1000 rpm or so I think, it doesn't run rough or anything. Everything seems fine, there's just a jerking/knocking sounds. Thanks for all your input