New to forum and Sea Doos Intermittent spark above idle thru WOT

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I am new to the forum. It was great to find this Mercury forum.
I have an engine problem or problems with my 2003 Islandia 240 EFI. I haven't had the boat long, I was cruising along at 2/3s throttle when forward motion was reduced as if I had throttled back, I hadn't, and the engine was running rough. The boat idled ok so I was able to make it out of the water.
When I got home, I checked the spark on all six coils with a spark bulb tester, all showed intermittent random spark above idle except for #4 coil which was dead. I replaced coil, now all 6 coils have intermittent random spark. The 20 amp coil fuse has also blown twice so far while testing coils. I have been using the 2002 Mercury 240 EFI service manual to do ohm testing. The sensors that one tests using ohm's are ok. Not sure how to test the other ones ie TPS, knock sensor and so on.
Any thoughts?
I am a shade tree mechanic, and would rather figure it out myself before spending money on labor.

Before get get too deep into it... I want to verify the engine. Either post the serial number, or a picture. The early build 2003 boats had the "2001" engines... the late 2003 boats had the "2001-1/2" engines.

But... intermittent spark on all to me is...

1) bad throttle guardian.

2) Bad kill tether.

3) Corrosion/bad connection on any common ignition part. (pull plugs apart, check, put back together)
IMG_1343.JPGIMG_1344.JPG Thanks for responding so quickly Dr. Honda. I'm including photo of engine and serial number as well. The serial # is 0E414501. What is the throttle guardian? And what can make it go bad?
It's a Gen 2 engine.

OK... the throttle guardian is a little box that Seadoo put in, so you can't rev the engine very high when in neutral or reverse. They eventually just fail. (No real reason) But, since they cause more issues than they solve... most people just yank them. It will be a black box in the helm. If you see it... just cut it loose, and toss it in the trash. While you are in the helm... verify that the kill switch on the lanyard is ok. (They go bad too) OR... verify that the rubber tip in the lanyard is in good shape. When they get old... it has a hard time holding the button in.
I checked and cleaned coil wiring to spark plug. My tether switch tested great continuity when pushed in, and I have a new lanyard. Could not find throttle guardian. I looked behind access point in changing area, saw lots of components, but no throttle guardian.
I tested engine after cleaning coil/plug and I still have same issues. Any thoughts on why 20 amp fuse for coils pops after a second of WOT? I've wonder if the TPS or even the stator/capacitor under flywheel might be causing the problems.
If you are popping the ignition fuse... then there is either a short in the wires... or you have a shorted coil.
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