Did you ever resolve this idling issue?
I have exactly the same issue even on the same cylinder.
I checked the sensor values with an OBD reader and all seems normal except for bank 2 Lambda sensors. I used OBD car doctor that draws a graph of the values. Everytime I feel the 'missfire' in the car the voltage levels on the 2 sensors drop to about 0.15V indicating almost no burnt or unburt fuel indicating a problem with the injector.

My next step is to connect the scope to see the waveform sent from the ECU, but if the ECU can just turn this signal off because it detected a missfire, the problem can be elsewhere...

Any advice?

Vehicle : Mercedes WDB2100622Bxxxxxx E240 2001