[staylor]

..sort of like the ones on my 2002 Opti 150, but with the large number of trolling hours I's change them anyway- making sure you get the right P/N- should be NGK IZFR5G. Torque to 20 ft-lbs- leaving lots of time to change the lowest plug on the port bank. After the plugs are in, wipe a very thin film of Merc 24c lube on the insulator so the boot doesn't weld itself in place over time. Make sure each plug wire is firmly on the plug- the 2 lower plugs on the port bank are known to be tough ones to get the wires seated. A plug wire that is not fully seated on the plug will cause just the miss that you have...and don't ask me how I know this!

While you're doing this, look at each coil terminal to make sure that no carbon "wires" or "hairs" have formed that can short the terminal. I had a Merc 2 years back with an intermittant miss that ended up due to a half inch long carbon hair that had built up over 8 years on one of the low voltage connections to the point that it was arcing out when I hit a wave.

I second ohiojmj's post about emptying out the water separator filter and re-installing it. If the plug change and draining the filter and checking the lines and primer plug doesn't fix it, then a trip to the dealer is needed to look for a bad coil or ECU- and hopefully it's not the ECU.
Doug