actually contrary to popular belief using water to clean your engine is not a bad thing. I have done it on all of our cars and I've never had a single problem contributed to using the water. You will want to however use plastic bags or something else that will work to cover the alternator, and the coil packs/ICM. It is o.k. to use cleaners and a garden hose, or a lower powered power washer to clean your engine. All of the electrical connectors are water tight just for this purpose. You just don't want to be Trying to get the water in there.
The best method I've seen is steam cleaning. Everything pretty much runs off of the engine with little water used. Most dealerships use this method to clean their engines before sales. My guess would also be with the coil packs, or the ignition module. It'* hard to just gues what your problem is though without actually seeing or hearing the car. I doubt it'* something mechanical though.