Well, since you're so desperate, I'll throw my non-mechanic, non-tech-expert $0.02 in.
MAS, done! Harness, done! Sounds like the usual suspects are already in jail!
My 'ol 190E 2.3 did the same thing, and I had trouble solving it too. Turned out in my case that the seal where the tube thingy connects to the throttle-body was worn out, and moisture was getting onto the throttle plate. Somehow, I have no idea of why, this caused the surging idle. My indie replaced the rubber thingy, and viola! it was fixed. Never came back.
Probably of no help, but ya never know...
1998 C230 "Black Betty"