Engine runs rough and eventually stalls.

P0420 is low cat. converter efficiency code stored because the cat has been "hollowed out" (illegal). What probably caused the cat converter to fail and may be causing the engine to stall is that the engine is running too rich a fuel mixture but that would have to be verified by looking at scan tool information and or looking at gas analyzer readings to see what CO and HC readings are. You would need a scan tool, gas analyzer or at least test instructions.Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online