When I use to detail cars back in the days, Id always put a degreaser on everything (let it soak for a few mins) and power washed it with what they had at the shop, just watch out for the distributor. A couple times the cars would run like ass until it dried out some, I think we always had the cars running when we did it. Just dont sit there and beat the hell out of things with crazy pressure for a period of time, the degrease will un-gack things and the pressure from the washer will help the more gacked up crap be removed.

Than we put this snotty like pink stuff on it and made the whole darn engine and plastics look fake and brand new as hell, but on a fake level!!

Not saying this is what everyone does, but at this one shop I worked at, thats what they did and it looked damn good after.