2000 Buick Regal 2000 Buick Regal stalls while driving/dece

My 2000 Buick Regal has died multiple times in the past week as I was driving. The engine quits in as little as five minutes, but might take longer, and always happens as I am decelerating (foot off the accelerator, applying brake). Cranking causes the engine to fire, but not enough to keep running. It might take up to twenty tries to get it running again, and black smoke pours out of the exhaust.

En route to my mechanic, driving slowly and gently, the car would not stall. The mechanic road tested the car, and he made it stall.

Initially, error codes P0300, P0463, P1096, P0103 and P0128 were read, but they were too disassociated to be of any use. The older battery was replaced and the cables serviced to ensure good positive and ground connections. The ECM was reprogrammed (cost: $100!), And the Regal ran well for a day. Shortly thereafter, it began dying as before, and was returned to the shop.

Mechanic Bob kept the Regal in his shop for four days, engine idling with test equipment attached. When it died, it started up immediately, and no error codes are present. He is at a loss.

He replaced the crankshaft sensor (at my urging), and it looked like the problem was solved. Not so! It only took a few miles for the problem to happen again.

The odometer light has not worked for several weeks, but I doubt if this is connected.

Anyone have any idea as to what might cause this?