EPC light 02 a4 quattro
 

I have a 2002 Audi A4 Quattro v6, the EPC light keeps coming on. The car had a bad exhaust leak when I got it, I recently fixed the leak over the past weekend and unhooked the batter to reset the dash. The car ran really rough when we got it idling anywhere from 800-1200 rpms, after I fixed the exhaust and reset the dash it ran fine for about a day then the car started running rough again stalling at red lights and not starting back up for 10 minutes cant seem to figure out where to go from here had a local auto parts store hook it up and is still giving a code for cat bank one. Any help is greatly appreciated