Ethanol and Rough Idle ???

I recently boaught a 19' Javelin with a 150 HP Johnson Faststrike from a friend. We took the boat out together for a test drive and the motor ran great. It continued to run great until I purchased gas in Maine that had ethanol in it. Now it still runs great once up on plane, but it sputters and coughs while idling. I put a can of seafoam in the gas tank and it seemed to help some, but I would like to have it idle even smoother.

I'm sure some of you have run into this before. Any advice would be greatly appreciated. Thanks in advance.

Could it be time for some new plugs. Also, the ethanol could have messed up the check valves in the fuel recirculation system. I believe that engine still has that type of system. Someone will correct me if I am wrong. Good Luck.