IAC / solenoid valve issues?

by Dave
(Port Richey fl)

Ok so I just bought a boat from a family member that hasn't taken it out in the last year.

The engine is a 2006 40 HP efi 4 stroke mercury. Model # 1A40412FD serial # 1B237952 .
I couldn't get the boat to run no matter what I did with using new gas and additives.
I noticed that I wasn't getting any gas out of the purge valve on the vapor canister. My wife grabbed a can of starting fluid and sprayed a little into the air intake and it fired right up then died just as quickly. Obviously the engine ran until the spray was no longer fueling the engine.
So I removed the vapor canister took out the fuel pressure regulator and the high pressure fuel pump. The filter on the HP pump was to no surprise all gunked up so I replaced the filter after soaking everything overnight in cleaner. I also hooked the HP pump up to a battery to make sure it wasn't stuck. I also replaced the inline fuel filter and cleaned the metal screen filter above the fuel pressure regulator which was also caked solid.
After doing all of that the engine will now start and run as long as the hose is disconnected from the solenoid valve (or what I call an IAC). The engine runs with very high rpms like this. As soon as the hose is reconnected it dies.
Does this sound like I need to replace the IAC (or hopefully clean that somehow)or should I put focus elswhere? I have called the mercury service line with absolute no help, as from my research these engines will have all kinds of issues after 3 months of sitting.