Hey guys, so I got the p0420 code recently and decided I would take my cat apart and clean it of its material. So I went through the trouble of taking off the exhause manifold and everything that goes along with it just to find out it had already been gutted. So whatever i put it all back together, and I went ahead and did the poor man spark plug anti fouler mod for the 02 sensor. Car runs fine and everything now but it's starting with a sputter like it wants to die and sometimes it does die other times it pulls through. I'm thinking maybe I didn't drill the hole for the 02 sensor wide enough. If you guys have any ideas help is appreciated.