About 45 seconds after I start the car, it just stops running. It putters and fights, but just stalls. After I restart, it never stalls again until it sits for a while. I am reading code P0420 as well. I called a local AM radio car show and they said the cat converter and the stalling should be independent events and to replace the electronic throttle bottle, which I did, and it still stalls. Maybe I need to calibrate?? I'm a DIY newbie and I am struggling here. Any thoughts please?