Idle problem

I have 2001 Bayliner 195 with a 4.3 merc I/O. Just bought it over the winter. First trip out with it all was fine. Ran like a charm. On second trip out yesterday I had a problem with the idle. It would idle at normal speed and then drop and come back to normal. It would do this over and over again. Also while doing this it would sometime let me accelerate and sometime would want to stall. And sometimes it would stall. She would always restart with no problem. When it first happened. I reved it up in neutral a few times and that seemed to make all this go away for a few minutes, but it came back again. We just about made it back to the dock. When we got home I put the muffs on it to flush out the seawater. Brought it up to operating temperature and it seemed to be running fine then. Only other symptom I can give is that it seemed to be at its worst when it was in gear and not just gunning it in neutral. Any help or ideas on what would be causing this would be great. Thank you in advance!!!

 

Well ide start with the fuel filters water traps etc etc

 

What is the fuel delivery system, 2bbl or 4bbl carb, EFI, etc?

 

I hdd the carb rebuilt, drained the old fuel and changed the filters and water seperator. All is good now!
Thanks everyone!