1990 300SE
Engine 103.981
Chassis 126.024

I too have been experiencing the same rough cold (meaning engine has not been started in 8 hours or more) start up as mentioned above. I just bring the rpms up manually to about 1000 after starting and hold the idle there for 15 seconds, and then I let off the pedal and the engine idles beautifully. I know this isn't a fix, but it does work for me.