175 Mercury Optimax Rough engine idle surging problem need help

[billeboy3]

ok so i have a 2006 175hp mercury optimax boat was running great killed the motor, then ran my 9.9hp kicker motor which is connected to a fuel water separator for both motors on the same main fuel tank, ran the kicker started right up cruised around then turned it off tilted it up done... go to start my 175 opti then all of a sudden was idling extremely rough and surging and chugging really badly then would die, restarted it same thing but put it into gear and kind of pushed through it and it seemed to run ok but could still hear the motor was struggling and not running right, bring it back down to idle and is violently surging while idling and then would die, starts again and can get it quickly into gear and run the motor but when i bring it down to low rpms it would start running extremely rough again is really a mystery to me and the mechanic, any suggestions would be greatly appreciated
* changed plugs
* changed fuel water separator
* tried fresh non ethanol fuel
* no codes
it is currently at boat mechanic and he's having troubles diagnosing the issue anyone have the same problem?

 

[lipripper334]

having the same problem on my 75 optimax runs great wide open or after I get it planned out but if I pull it out of gear it idles rough and dies.i changed the fuel water separator and plugs to and that made it plane out fast and even gave me a lil more topend but now this idle thing started. let me know if you find out and thing. the closes I could find was bad reeds and I hope its not that