Have you tried replacing the fuse in the overvoltage protection relay? Do a search on this board with the words "overvoltage" or "relay". You will find some interesting stuff that might sound familiar to your symptoms...
Also, I remember someone with a car like yours (and mine) that had the electro-hydraulic something or other replaced that worked wonders on the driveability of his car.
Good luck bro.
1989 300 E
1992 190-E 2.3