Use Gunk or similar-spray on engine cleaner with a warm, not hot engine, soak for few minutes and rinse with a hose. First cover your choice of electrical connections. You may need to agitate greasy areas with a brush before your rinse. I also use a wash mit with car wash soap to wash off the areas reachable.
Then spray with Aerospace 303 on plastic parts and wipe off.
Thanks,
1995 525i Auto, M50TU 2.5L, EAT chip, 1/95 build, USA, 205/65/15 tires, ASC+T, HID, lumbar, EC Mirror, BMW Alpine 5 radio with BMW-Pioneer CD Changer, abt 236k miles, Oxford Green/Parchment