I know my car needs a new cat.converter. It has dual cats. One has been replace by the previous owner. And the other is still the original. But my car is now backfiring a little and it kinda smells like gas. When my car gets hot I can feel my car shake and backfire a little on a red light. It also Idles up and down between 1-0 rpms. Do I really need a cat that bad now? Prior to this my budding checked the ecm and it said that the egr valve was bad, but he advised me to change the cat. converter first.