Use a solvent cleaner to break down the grease and road film (let it sit) then rinse off with very light water pressure. Let it dry completely then use a foaming tire spray and let that sit then wipe off excess. This leaves a nice shine on the rubber and protects it. Also you can use goo gone and elbow grease on the paint expecially on the underside of the hood. The procedure I used when I worked at a detailing shop.
DO NOT USE FORCED AIR!!!! it pushes the water into wireing and other parts and WILL damage them
E30 Stuff For Sale: Clutch Fan and Shroud, 4 Pack Ignition Coils, ATE 750il MC (New), Offset Trailing Arm Bushings, m42 Valve Cover (Clean), M10 Engine Mounts (New), M42 Injectors,