Any check engine light?
Sounds like it could be wet spark plugs too. Thoroughly check the plug holes for any water.. if there is any, do *NOT* remove the spark plugs, otherwise the water will get into the cylinders. Dry the holes with paper towels or something, then inspect the spark plugs once you're sure the holes are try. If they're wet, I'd replace them.
Also inspect/check the plug wires for arcing.
Be VERY careful with this because if you get ANY extra water into your cylinders you can easily destroy your engine.