The first thing I would check would be the charging system. On my E320 when the alternator was on its way out I was in stop and go traffic and it started doing something that may be similar to the experience you are having. I will say though that the first sign something was wrong is that the radio would shut off and the power antenna would lower then the car started driving real strange. This may be what is called the "limp home" mode. I don't know. The other problem, especially on the W124, is the wiring harness. Give it time and see what one of the techs say.