How about ignition getting wet??

Wait till dark, engine completely cold, get a windex bottle with water. Start the engine, turn off all the lights. Look for any arcing along the plug wires or at the distributor cap. Spray water, see if that makes it arc. It might look like a dull blue glow.

If you see any of this, get new plug wires or cap & rotor, whichever is arcing.