The best way to clean an engine bay is a matter of opinion. Some people like to use spray cleaners like "Gunk off" I dunno even that'a even the right term.
I personally don't like the chemically cleaners because I am paranoid about breathing in fumes too much and melting my lungs. Before I do anything I wrap my the filter on my intake with a plastic shopping bag to make sure it stays dry. I like to mist my engine (cold, never after its been runnning) with Simple Green. I let the SG sit and do its work for about 2-3 minutes. Then I hose down the motor with the nozzle set on mist, but I make sure to never spray anything directly. After that I mist over the entire engine bay with Meguiar's Vinyl & Rubber cleaner. I wipe off the metal parts like the fuel rail, the top of the PCM and a few other pieces so that they don't get spotted. I let the car sit for another 20 minutes then take it for a spin and let the heat of the motor take care of the rest. Open the hood afterward and everything is nice anc clean & shiny :sun: