Does your car only idle bad when its cold? Apparently, this is a common phenomenon with 400E's that I read about. Mine sometimes idles rough too, even surges up and down for a few seconds, but smooths out eventually. It looks like you replaced everything that it could be. Alot of 400E owners just live with it. How bad is it?
As far as the Tranny switch and the brake lamp switch, they really have nothing to do with your idle. Does your 400 have ASR? Those parts are only under a microscope if you are having ASR problems, such as ASR light coming on and/or limp home mode. They dont affect idle smoothness.
I see that you went for the "hammer" look for your car
, thats exactly what i want to do. Can you send me some pictures? Where did you get most of the parts, like the AMG skirt, headlights, etc.