How about the valve guide seals?
When I had my '93 190E, I had the same exact problem you are speaking of, especially when starting the car. When operating, it was OK, but when I would stop or the car would idle, it would get dangerously close to dying, and sometimes would.
Had new valve guide seals put in, and the problem went away. I dunno - maybe I had more problems than I knew, but just thought I'd post what fixed my problem.
The 190E is a great little car ... I miss mine, but my C230K is a big improvement.
Best of luck,
Michael