I just found a loose connection between the header and the down pipe. Since snugging that back up, I've noticed that the idle problem has been showing up MUCH less frequently. I suspect the smog test would have been a bit better, too.

However... I've still got that funky after market cat on there. It's going to be replaced with a new one. I was going to eat it and just buy an OEM cat, but I've been informed of a new law in CA that appears to have required aftermarket cats to be much more efficient. I'm going to have to check one out and see how it compares to OEM. But that's a smog issue, not an idle issue.

If I ever figure out the idle stuff, I'll be sure to post. For now, I'm at a loss.