2002 Pontiac Firebird Rough Idle when wet, no engine power

Whenever my car's engine gets wet, it starts idling really rough and the I don't have much engine power and the "check engine light" comes on. It doesn't happen when I first crank the car (for example, in the morning) but when I go home at night, it's pretty bad. I also have a little bit more smoke coming out the exhaust than I think is normal, but that was just when I first cranked it up this morning.

background information.I just put a new throttle body assembly on it and the transmission is only 2 years old. The fuel filter is only a few months old as well. The fuel pump and water pump are only 2 or 3 years old and the alternator is brand new also(less thank 6 months old). I also just had the spark plugs changed.