Grab the rigging cable,(battery Cable) put it next to your ear and bend it. Does it crackle? Yes, the cable is bad. Common.

The X dimension is different between the B2 and B3. Fix your drive. Simple repair.

Do not use a torch, no matter what.

First thing to inspect. Where the rigging comes into the engine cowling, remove the hold down for the cables, fuel line, battery cables ect.. an look for corrosion that is pinching off the fuel line....

I would use OEM or CDI. Not the cheapest one on the internet. Marineengine.com, where you are asking for advice, is where you should get your parts.

Common issue. Replace it.

Is the name on this boat "Hold fast"?

Why do I feel like I know this boat. Can you post a picture?

2X's on the injector rack.... Check boost, check linkage......

Pressure test it. You will see what is leaking.

The IAC goes open when running at cruise speed. So it should not cause a surge at cruise speed.

Where did the last tech get the IAC? Automotive IAC will not work on this... I don't care what anyone tells you, the PWM% will be way to high with the auto parts store equivalent.

Look for...

How about throwing a new set of plugs in and retesting. You cannot clean spark plugs. Chances are this is your issue. Doing all the other things on your list first is not how you go about it.

Where did you purchase the new IAC from?

Re-indexing the HVS(distributor) clears up a lot off issues with Idle on a 555 MPI.

Find a good mechanic.

Mercruiser has an updated Lube Monitor bottle for this issue. First, I would go through the drive and make sure it isn't eating itself. If everything looks good the bigger bottle will help with the...

First thing you do with this engine after the fuel filters have been changed is replace the spark plugs making sure they are the OE recommended plugs. (Always the first thing.) Then retest.

If your the dist pick up is bad it will lock the engine up like the timing is at full advance.

Put all the plugs in Pull the coil wire and ground it see if it cranks freely.

I watched your...

Disconnect the coil and see if it crank with the starter.

Your yellow w/Purple stripe started out life as a Yellow w/red stripe. This is the wire that feeds power to the start circuit.

Your red wire from the switch panel is feeding power to the...

Start the engine. You were told wrong.