This is a common problem and my now sold 1990 300E had it when I bought it. Some times it would idle very rough for a few seconds and then stalled or it just stalled. It happened only on warm starts, not on cold or hot starts.

There are many potential causes and one of them is a slightly clogged injector(s). Some fuel will leak into the cylinder and when you start warm, there is too much fuel so it stalls. If it sits long enough, the fuel evaporates so it starts and runs. If you start hot, there is not enough fuel leaked so it starts fine as well.

I lived with it but I used one bottle of Techron per oil change (right before oil changes). After a good a year and a half, it eventually disappeared. It then ran without this problem for 3+ more years before I sold the car.

Vapor lock in the fuel system is another potential cause.

Clean injectors (use injector cleaner regularly) and clean combustion areas (change oil frequently) are key to the smooth running and start of cars. Among the 4 MBs I bought, the longer I keep them, the smoother they run and start.