i have the same problem with my 190e2.6, and the problem manifests only when the engine is hot and ambient temp is not cold (i.e., spring or summer - no problem in winter, thanks).

no problem starting, but have very rough idling up to about 2000rpm, and i have to let the engine "clear its throat" before moving out.

once on the move, even during idling in traffic, the problem does not resurface. Seems like a fuel delivery problem to me at hot startup, like the pump or reservoir not being primed, or being vapor-locked due to the heat.