I have the same problem and it's been driving me nuts. I replaced the spark plugs, cap, rotor, OVP, fuel distributor (had a couple of spares) and finally, the fuel filter. Had some improvements now reading this I have to go replace the fuel accumulator.maybe the fuel pump. Hopefully my catalytic converter is not clogged.
Vehicle- 190E 2.6 Sportline

I replaced both fuel pumps and the fuel accumulator, The catalytic converter was good still the problem was there.....I replaced the fuel injectors and the car ran much better after that.