Engine Dies. Sputters

[muskyfins]

2011 Formula 290 SS
350 Mag MPI
SN 1A619395
654 hours
Lakes were no wake due to high water. Idled out to our spot (6 miles) no issues. Idled back with no issues.
While docking, port motor died. Tried to restart. Starts, but stutter and stumbles hard. Can't add throttle or she dies. Pull back throttle and starts to come up to normal but sputters and dies anyway.
Starboard motor has no issues. Spark plugs have 30 or so hours on them. No audible alarms. Haven't scanned motor yet. Always run premium fuel.
What do you think? I'm thinking IAC due to 12 miles of idle speed. Second guess is HP fuel pump?

 

[alldodge]

Don't know what to think without testing, but IAC would not be first thought because it will start without giving more throttle.

Looks like you have a EC (Cats) motor. The easy check is the pressure at the rail, but do get it checked if a scanner is available

Running premium gas just cost you more and provides a tad less power, and might cause other things do to incomplete burning of fuel. Your motors only need 87 and will run better