* The symptoms you describe in your first post sound exactly like ones I had with a '93 600SEL (W140, M120). The EA/CC code turned out to be a simple cable adjustment. The main problem was an obstructed catalytic converter, the right side in this case. The obstruction became worse and worse over time; i.e. the performance didn't go bad one day and stay bad. It was on and off, irregularly. Then more often. Then finally all the time.
* In the case of this v12, the right cat was also very rusted inside. So one day, after the bad performance was constant, the exhaust back pressure blew a hole in the rusted cat, making it hiss like a steam boiler about ready to blow! Taking care of the leaking (clogged) cat also brought back the performance. The customer was impressed.