1992 MB 300sl Stalling 3 litre straight six.

My car with about 140,000 starts OK, but after a cold start often stalls, (with the battery light coming on) after the first 5 minutes of driving. It then restarts and is then usually OK for the rest of the day. I've replaced the distributor cap, the ignition wires, the spark plugs, the overload protection relay, all the fuel injectors and had fuel moisture remover added to the fuel tank. The car runs very well but still stalls. Any ideas? My mechanic is not returning my phone calls. Thanks