Hi what you're having sounds more like a mechanical problem, fuel is not
injected in time or the engine running too lean or something, I don't know
much about that I'm afraid, try AudiWorld.com. My problem is to do with the
Audi immobiliser system, when you insert a key (which has a microchip) the
reader coil sends a signal to the key and checks its ID, if that fails to
bounce back or gives a wrong ID it will flash a key icon on the dash and
will not let you start the car, to be precise it lets you start the car but
cuts it out after 2 seconds (why this way however I don't know). On earlier
models, the reader coil fails after about 6-7 years of everyday use, for no
specific cause the problem will almost certainly occur. It's a design fault
in my opinion but I don't think Audi will admit that. They can replace the
reader coil and recode the keys for you at a charge, probably about 100-200
UK pounds, roughly 80-160 US$ I estimate.
Hope you'll get your car fixed soon with little cost/hassle.