Ok, here goes. Last fall, getting ready for winter storage, I added stabilizer to my fuel and went out and ran the boat a couple of times to get it circulated. Just before pulling out of the water, the engine developed a miss. At idle you cant hear for feel it, but under load, it misses terribly. It cleans out once you get it up and on plane. Almost sounds like a plug wire(s) breaking down (engine has 260 hours). Just curious if stabilizer would foul the plugs or if it would cause the fuel filter to clog reducing flow. Doesn't make sense to me. It ran perfect all season, but didn't start this until i added stablizer. I am going to change the filter and water pump before season starts. Will probably pull the plugs and replace them as well. Any thoughts would be greatly appreciated.

Fuel Stabilizer should not cause anything like that.

was it cold out when you drove the boat?

Air temp was high 60's, low 70's. Water temp was probably in the same ball park.

My 525 EFI did something similar last summer. It would idle just fine, hesitate, backfire, miss, when applying thottle, and then clear itself out and run ok in mid to upper rpm range ... ended up being a MAP sensor going bad. No alarms, at first, but it kept getting worse throughout the day until it started giving an intermittent alarm code (can't remember the number of beeps in the sequence anymore) but the manual listed a variety of sensors that had that alarm code sequence. When they put it on diacom, it showed a bad MAP sensor. They installed a new one and it instantly ran fine again. Not saying that is your problem, but that is what my engine did, and that was the sensor that was bad. Several of "us" were betting it was a bad IAC. Have it scanned and see what codes are stored, if any.

Hook it up to the scan tool under load and find the miss or stumble. Don't guess, you'll only be 50% right on a guess at best!

Best Regards,
Ray @ Raylar