there is ABSOLUTELY no problem with submerging external engine parts in water. anything that must not get wet under your hood is already waterproof (distributor cap, electronic devices) everything is sealed so that things that must not get wet won't take humidity. if your car does'nt work well after that wash, it's because something was ALREADY broken and should have been repaired. you can even think of it like an ultimate performance test to know if everything is in order!!!
O.k. enough talking, go get that powerplant clean!!!