1987 Volkswagen Van no power, no idle

i had misfires and the belts ran off in sandiego. got the belts back on, changed the wires, plugs, cap rotor. engine starts fine. after about a minute or so the engine stalls. starts up alright, but no power and stalls at every intersection unless i push the accelerator pedal and keep it at 900 rpm orso. checked timing, swapped mass airflow, changed coolant sensor, same problem.
first time this ever happened. before i changed the airflowmeter and it was fine. it seems fuel is okay at start and then gets too rich.
jay k.