Mercury 90hp 2 stroke has me at ropes end!

[Mad Problems]

hey guys i have mad problems! my 2006 90 optimax has a hard time cranking and when it does it idles rough (dies if i don't give it gas). when i put the throttle down it sounds like a valve is sticking. I can't figure it out.
i changed all three coils, fuel filter, spark plugs and the problem will not go away.

does anybody have any advice on what to do? please help. the motor has always worked great with no issues but i am not smart with motors.