hey i'm wondering what to use when detailing plastic parts in engine bay ? any ideas ?

I just use an old rag with some degreaser. Spray some on the rag and wipe the plastic that needs cleaning. Shouldn't really damage it. I guess you can remove the part you want to clean and use soapy water, but it will just get dirty again after a drive or 2.

Once you've cleaned them, quickly go over them with a coat or two of Tyre/Vinyl Shine to give them a nice, glossy, protective coating.

This stuff attracts dust like no tomorrow, avoid using it in the engine bay. As shongus has said, just a clean cloth. IF you get really keen, you may want to look at getting them cleared, but you will still be wiping then down all the time.

Dust is going to be in the engine bay one way or another. I've been using Vinyl shine in my car's engine bay since January and have only have to wash it down once in the last 10 months from a light coat of dust at best. All personal preference; I myself prefer a cleaner and newer look to my car -- clear coating would be a waste of time as you'd have to plastic prime, coat in the colour of your choice and then clear coat it and unless you're using a 2K Clear, you'll have to buff it to get a decent gloss level out of it anyway, especially if its an acrylic clear.

303 Aerospace FTW!