2000 Nissan Maxima with CEL and rough idle

My Maxima has a check engine light illuminated. Normally, the cars runs fine but every occasionally in extremely humid conditions and when the temperature is around 50 degrees (F), the idle gets extremely rough. I had the fault codes read and they were P1320 (three times) and P0420 (once). After being read, the codes were reset, but immediately returned. The weather was exactly as described above. The car has 36K miles and is driven around 4K miles per year. Any recommendations for repair? Could a sensor be causing the problem? How about a defective wire or plug? If so, where is it located, and how difficult would it be to replace the defective part? Thanks for your help. Bill

Since you have noticed the problem in humid conditions, your problem is almost guaranteed to be in the high voltage portion of the ignition system. You could try spraying water from a glass cleaner bottle on various parts of the ignition system and see when the rough idle starts.

I believe that Nissan had a batch of flaky ignition coils on 2000 Maximas, so I would not be surprised if that is your problem.

READ THE responses to your post of yesterday. I RESEARCHED the trouble codes and put my findings on that post. Nissan was aware of those problems. They put out fix instructions in Service Bulletins. Your questions have been answered.
A recap: change the ignition coil(s), and have the engine computer reprogrammed.