Sounds to me like a clogged catalytic converter. Allows the motor to run a bit while its cold but when the catalyst and the gunk stuck in it heats up and expands, causes enough restriction to choke your motor. Easy way to find out is to loosen the exhaust pipe before the cat just a little and run it (it'll be a little loud). If the car drives fine with the exhaust flowing freely through the gap, then you've got your answer. If it still behaves the same way, then start checking your timing on the cams.