what would the engineon a 2001 buick century to die after accererating 200 feet past a green light

You might have either a problem with the Idle Air Control Valve, IACV, or the fuel pressure may be low. You can test the fuel pressure with a special tool you can get on laon form Adavance Auto or Auto Zone. While you are there, have them pull the trouble codes as well because that will help diagnose the problem and it's free.

Also check your Spark plug wires, and if necessary have them replaced. They may not look bad, but this can happen on these cars and is an often overlooked problem. Had this problem on a similar car, most often associated with toll plazas and stop lights.

Failed spark plug wires are most likely going to cause an issue like misfiring. Stalling out after sitting and then taking off is more associated with a fuel delivery problem.
Again, test the fuel pressure as this still is a fuel delivery issue associated with fuel pressure.