99 Jetta Won't Start When Wet!

I have a 99 Jetta Wolfsburg Ed, III body style, auto, 2.0L, 38K miles only. Whenever it rains or I wash the car it won't start or will run extremely rough and have no power. Usually it will not start at all, not even a sputter. I have to wait until the car is totally dry before it will run normally again. (No Check Engine Light either). I have replaced all the spark plugs and wires, as well as the distributor rotor and cap because I thought there may be a short or a crack there but the problem just happened again. What is causing this? Has this happened to anybody else? Something is obviously getting wet or damp but I haven't found what it is yet. Any help greatly appreciated.

Check for the infamous bad coil. It will arc to ground when wet.