I can't figure this one out and I don't know why it started all of a sudden but here are the symptoms:
1) Rough idle.
2) Very little power on acceleration with stumbling
3) The car is okay when going over 35 mph but below that when I slow down for a stop it stumbles and either stalls or gets very close to stalling.
4) The exhaust has minor backfires and seems to be emitting more exhaust than normal.

This is what I've done so far:
1) Spark plug one seems okay. Spark Plug four(closest to the interior) seemed fine but the threading seemed to have oil on it. I also noticed that there was a buildup of oil in the area around the sparkplug on the engine casing. I'm not an expert at diagnosing sparkplugs but it seemed suspicious.
2) The Fuel pump appears to be functioning, I can hear it humming when I create a relay between circuit 4 and 6 as recommended by Haynes manual.
3) I do not see any bad grounds.
4) The air filter was replaced and is not a problem.
5) I can't find any air leaks, although I don't know of a great system in locating them.

I'm now trying to run the fuel injection systems tests but I cannot seem to depressurize the system. Haynes says to pull the fuel pump circuits, turn the car over and wait for it to stall. My 240 will not stall after 15 minutes so I'm a little hesitant to do the checks until it depressurizes. Any advice here would be greatly appreciated.

My plan of action is to replace the fuel filter and then possibly the fuel pump.
The carberatour is out of my expertise and I am looking at other possiblites before addressing it. Does anyone know of any good tests to check for a functioning carberatour?

Otherwise does anyone have any ideas of what else to check? I'm afraid that I'm missing something obvious. Is my plan of action logical?
One other detail: three days ago I drove through two feet of water. The next day I drove for hours and the car was fine. Later that day though the problems arose. The air filter was wet, I changed it but the conditions did not improve.

If anyone has any ides I'd really appreciate the help. I'd like to repair this myself but its looking more and more like a job for the mechanic.
Thanks for reading.