you need a cat. get a good quality cat not a cheap one. after it is repaired, it needs to be driven to see if the missfire goes away. the 101 is a mass air flow code but doesn not mean it needs to be replaced. have it checked first

Roy

Which cat would this be referring to? There's one connected to the exhaust manifold itself on the 2.4l and then there is either another one before the muffler or a resonator...only saw sensors near the first one.