Flyshifter11

Hi there I have an 09 plate ford focus and my engine management light came on and it flashed abit earlier so I done a bit of research and it seems my coil pack and spark plug are shot. One guy said when that happened to him it was un burnt fuel getting into his cat converter ? Im just looking for a bit of advice because I just bought the car from a garage last week and they put a years MOT on it but is that something that should have been picked up on an MOT ? It also idles weird as in seems abit judery.

thanks for reading