I've had this problem since I bought the car. 98 2.5 mtx 137,000 miles. Everytime it rains I get what feels like a misfire. It only does it during heavy rain, which we get alot of in Ohio. Does not do it in the snow or when its nice out. I've changed the plugs (Motorcraft) and the wires (Ford Racing 9mm). I'm not getting a CEL or any codes. The problem is not as bad as it was with the new plugs and wires installed, but it is still there.