one time i just sprayed a can and a half of GUNK degreaser all over the engine bay, and then hosed it all off. i ddint cover anything or dry anything off after that, and i just let it sit over night. the next morning, drove to work it drove liek absolute CRAP. it felt like an intercooler hose had popped off or something, and it was running super rich. it drove so bad for a week or so that i was taking my dad's car to work, and i couldnt figure out what could be bad. one day i got in and started it up, and it ran fine. well, it ran just like it did BEFORE the engine cleaning. i guess something just stayed wet for a while and was messing something up, anyways havnt had a problem like that since

i would cover important things though, like sensors, alternator, sparkplug wells, distibuter, those types of things. if you dont want to go through all that trouble, just dont soak those areas with water. a friend of mine washed his car very meticulously, didnt use a hose, but degreaser, a water bottle, and a scrub brush. took him like 2 hours though