My car (85 190E2.3) has a similar problem. It was very pronounced earlier - then the oxygen sensor was changed, and that smoothed it out 90%. But a little bit still remains. BTW, all standard culprits have been changed - cap/rotor, plugs, wires, injectors, filters, etc. One tech said its the mass air sensor - haven't gotten it changed yet as the problem has drastically reduced with the new oxygen sensor.
Hence I am curious to know the cause of this problem in your case - maybe it can help me solve my problem! BTW, is your gas mileage OK? Mine had dropped, but is back to almost normal with the new O2 sensor.