Well, maybe there is a crack in one of the vacuum elbows and it is not allowing for a full 100% of the time vacuum leak. The motor might be producing enough vacuum to seal the problem for a second, then the air gets in or something. Seen it on a different car, that's why I thought that first. Your post makes it seem like it has a weird idle all the time, except for the one minute sometimes, correct?

I also thought the Opti, as stated above, but I'm not sure. Every opti I have heard going bad has been a misfire, not an erratic idle. Not that I am an expert or anything though.

To me, erratic idle means air problem somewhere. I would think mass air flow meter before the opti personally.

How many miles are on the car?