I would of searched this but cant find the search bar. I have 05 GT cat was pluged so bolted new one on and good to go right...well for a few trips all was good..keep getting P0420 and desided to change rear O2 cause it was switching just like front one. started to un thread it and got stuck so just left it in and now when sitting idling for very short time and give er a shot of gas i could smoke out the whole parking lot anyone got any ideas what is going on? Oh ya this car is new to me so dont know any of the history