learn something new everyday! I think it just came in handy for someone I've been experiencing a somewhat similar problem the last couple days. Cleaned all the typical stuff to clean and temporarily removed catalytic converter and tested to no avail. My symptoms seem like this ect is bad on my car after reading this. I was sure it was the converter due to the mileage increase and occasional rotten egg smell when it was acting up. Now it all makes sense! Rotten egg smell most likely due to the fact that too much unspent gas is being dumped into it. After I verified the cat was good I was a little stumped, but I was thinking whatever is wrong is causing the timing to retard.

If this is not the problem I'll post my findings if/when I make them