Jesus that sucks!:mad: Who could balme you for being frustrated!
OK, Here is another goofy stab at getting somewhere with this motor of yours.
1) Try to swap computers from one to the other and see if the same thing happens on the other motor.
2)Another swap-your MAP sensors.
3)Sounds dumb but check your grounds in the engine bay and also at your fuse box(s). I was having a problem with the motor dieing during a hard wake hit and I found a loose ground in my fuse box. All it takes is one small disconnection and the ECM will lose all running memory for that split second to shut down the motor.
4)If this happens often for you, try to see where the fuel pressure is when she dies and try to confirm if the fuel pressure is always the cause(low). Then you can start picking apart the fuel system.
I'm assuming that the merc dealer scanned the boat for you to look for codes. At least in the MAP sensors case, it may not throw a code if it's shot. Did they run the boat with the scan tool on to check what all the sensors were doing. I just cant believe that this is something major causing this! Well if the computer is bad that may be a bit major$$$$$$$$$ :p
Keep up the faith, you'll find it:D Keep in touch! Scott

Yeh, the mechanic ran it for about an hour & no codes appearred. Of course, the only thing it did do was "the idle surge". Never found a reason for that either!! All components were switched also, even the module in the distributor. Go figure!! It has not died running on the lake at 3000 rpm in about 3 weeks, so maybe that phantom may be gone. Maybe I should get a priest and do an exorcism!!:(

LOL:D :D :D
BY THE GRACE OF GOD AND ALL WATER WETTER
HELP BLOWN FORMULAS MOTOR RUN BETTER
ALL MOTOR NEEDS IS A SPIRITUAL TOUCH
GIVE HIM A HAND HE'S NOT ASKING FOR MUCH
AND WHILE YOUR AT IT HELP ME GO FASTER
SO I CAN CHANGE MY NAME MR BAJA BLASTER
THIS ENDS OUR PRAYER ON THIS FINE BOATING DAY
ALL PROBLEMS SOLVED-JUST COME HERE AND PRAY!:p

OK, you are healed. Now check the fuel system!:mad: