I have a 2001 Audi Avant that that surges, especially when stopped at a light. It threatens to stall unless I rev the rpms. Could this be related to oxygen sensors?

Normally o2sensors will not cause this type of run problem surging can be caused by vacume leak or idle control valve

No this is not related to O2 sensors usually this i srelated to the idle position sensor. it could also be a bad knock sensor on the transmition going bad. I would replace the idle sensor first as it will cost the least to get.