Submerged gt40 engine, help

So, sank my ‘99 Super Sport (long story involving too much ballast and rough water). Anyway, engine not started or turned over until water removed from oil sump. Removed plugs and turned over to expel water from cylinders...not much. Disconnected most electrical connections and sprayed with contact cleaner, including engine computer. Dried with compressed air. Distributor is very corroded under cap, cleaned cap posts and rotor...sprayed with wd40 on inside of distributor.

Engine fired up, but ran rough. Seemed to smooth out a little over time(as engine warmed). Changed oil three times. Lake tested a day later and started right up, but idled rough. Would rev freely in neutral. Got boat up to speed and ran fine at steady throttle..about 25 mph, 3000 rpm or so. Would take large throttle inputs with a bit of hesitation and stumbling. Ran for about 10 minutes at speed. Temp Normal. Brought to idle and engine stumbles and quits. Restart is difficult and engine does not want to idle. Can start with cracked throttle, but quits soon after back to idle. If I get it in gear and attempt to accelerate before it quits, it won’t take the throttle and stumbles bad. Will rev ok in neutral, but not perfectly smooth.

What should I look for next? Or troubleshoot recommendations welcomed. TIA

No, I don’t think so. Boat was not totally submerged. Just back corner for a few minutes. But, the tank was under water for sure....but I would think tank sealed well enough to keep water out.

I thought about opening the plug on the bottom of the FCC canister and seeing if water comes out

Better also verify zero water in the Transmission.
Years ago I bought a car and found it had water in the gas tank.
I had to run alcohol through the tank several times till all cleared up.
That was with a carburetor.
With your fuel injected engine I would put a quart of transmission fluid, ATF in a full tank and repeat this for the first 3 tanks of gas. It helps lubricate your injectors that will not like water coming through. It does not make the engine smoke or give you any symtems at all but it can help lubricate.
We sank my brothers boat one day, same issue heavy load and unexpected wind, engine stalled and waves quickly came over the back, lucky we got within about 20 feet of shore so it sank in about 5 foot of water.   We got it up, towed it home and worked several hours that night draining the oil and gas.   Went out and skied the very next morning with no issues at all. This too was before fuel injection and computers.

Lesson learned from the old 4wd days, using WD 40 to remove moisture from the distributor does work to fire it up and get you home but the fix is short term.
In my case it lasted about 2 weeks with my daily driver before my engine died. The oil residue in the cap causes it to attract dirt which grimes things up pretty quick and you will be stranded again.

David F wrote: So, how would water get in the fuel tank. Tank vent never below water.

Sounds like you answered your own question

Replaced MAP sensor and engine is back to normal. I guess the sensor, which is open to atmosphere and thus wate,r does not like being submerged.

Incidentally, I tested the TPS with my VROM and it behaved normally.

You say Distributor? May have cracked after clean out/start up from steam/moisture? Cheap experiment? Good Luck.

New MAP part number matched the one I removed: E67F-9F479-A2A. Got the sensor from Spark Surplus for $24.95.