cover everything you can and especially the mass air flow sensor.
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I have had good luck with my 07 BMW engine cleanings. I cover all the electricals with the plastic wrap/foil technique and go nuts on everything else. I do NOT use a pressure washer as i don't want to force water anywhere. I cover up the sensitives, hose it down pretty good and then use Megs Super degreaser at about 2:1...i know, i know, maybe too potent but haven't had any issues for a few years now. I let that dwell for a couple of minutes then work around with my brushes and rinse down. A good blow dry and an engine start to help heat up some things and make sure i haven't thrown any codes.
Done.