I have a similar problem with my 1990 300CE. Have changed practically all ignition components, fuel distributor, injectors/seals/
I just replaced my igntion wire set and bought is from www.kingsborne.com,
they make good set. Also, cleaned all electrical contacts, replaced all fuses too. I also found that by reducing spark plug gap from 0.030 to 0.025 made the car run much smoother. I do know that 92-95 300CE has faulty engine wiring harness, MB had changed their manufacturer, expensive item.
It seems that this is a common problem in 300CE.
Any one have any success??