When my 1897 190E Benz is started each morning it runs very roughly and frequently stalls out when the transmission is put into reverse or drive. Strangely, if I wait about 30 minutes and try it again the car runs fine. The only thing I can add is when I unscrew the gas cap there is a significant sucking sound (is there a venting issue?). Things I suspect are condensation in the fuel delivery system or perhaps a cold start sensor.

Anyone have any ideas?