the idling roughness can be due to 2 things - worn engine mounts and the known M103 idle misfiring problem.

when my 190e2.6 engine is hot (e.g., in summer after starting the engine hot), aside from the idling misfire problem, i even have the misfiring when i rev it, until around 2000 rpm, when it goes away. The best indicator of this is the ecomomy gage showing engine load, with the computer trying to maintain idle speed.

this symptom is very intermittent, but only happens when the engine is hot.

my car has a 5speed manual transmission, and I experience the driveline windup (rubber-banding) not only when carelessly letting the clutch out abruptly, but also when I am on the gas (i.e., driveline is under load) and the rear wheels go over a bump measuring around 2-3inches high by 6inches wide in cross-section. I have always wondered why this happens. So on roads I am familiar with, that have such types of bumps, I let go of the gas when the rears go over the bump (i.e., unload the driveline).
This does not happen in a car with an automatic because of the absorptive action of the torque converter.