Mark,

I have exactly the same problem as you.

I was lucky however, because I made the adjustments already on mine, and then it went out.

I was getting it ready for my EPA/SMOG test. I was lucky it passed OK.
I have 215K miles with the same Catalytic converter?

However I'm very interested in what the issue is now.

I'm hoping its not a CPU problem.

If you come up with anything let me know

Brian