hi all. i'm new to subaru vehicles and my 2003 wrx wagon is my first. i got it 3 days ago and this morning i got code P0420. i noticed a bit of a rough idle since i test drove it, but i figured it was something minor that a sparkplug change would fix. the car has around 85,300 miles. from what i can tell the muffler is a flowmaster with a magnaflow tip, but everything before that is stock (i may be wrong). i got it scanned at autozone.
i'm posting a pic of the engine bay to see if you guys can spot any culprits.
i hope its nothing major . thanks for your help.