I don't know much about your model year but if the computer is holding the wastegate open, you won't get any boost and there won't be enough air to burn the supplied fuel, resulting in black smoke. A stuck open wastegate shouldn't cause stalling though, just a lack of power.

__________________
Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo