[Devast]

I recently got my 2000 ETC back from having the A/C redone (compressor and blower). When I picked the car up it was misfiring. Had run perfectly when I dropped it off. The guy who did my ac, a friend who is a Ford mechanic, said it was misfiring on #3. He checked and cleaned the plug but it immediately misfired again. His opinion is that the Cat is bad and back-pressure is causing the misfire. He suggests I get it replaced, then tune it up. (apparently they are the original plugs so with 110Kmi it needs to be done anyway)

I always figured it was misfires that caused the cat to go bad, not the other way around. What do you all think about this? Do you think a fried cat can cause this type of misfire? Should I replace the Cat, or should I do the tune up first? Obviously Im confused.

If its any help the OBD is showing current codes: P0134 P0300 P1359 B0856

Any advice is appreciated.

TQP