2001 5.4
truck ran fine on thursday, parked it in the drive with the front pointed down the hill. Had torential rains that night. Friday morning the engine ran real rough, thought maybe something got wet. Continued to run rough all day and then threw code PO306, miss fire #6. I replaced the coil and plug with no improvement. Looked for vacuum leak and couldnt find any even with the use of starter fluid. engine shutters at low rpm especially under a load, clears up somewhat as rpm increases but it still surges if held at a steady rpm. I'm at a loss as what to look for. Is it possible that water got into the tank and thats what is causing the problem.
Desperately need to get this fixed and cant afford taking it to a shop. Any ideas?

 

Start simple; put some Iso Heat or Sea Foam in the tank to see if it will clear up any possible water in the tank.