Aah, you guys may have a point, the highest pump gas available here in California is 91 octane which I've always used. Chevron, 76, or Mobil. I also try to use the stations that have a seperate nozzle for each grade of gas to avoid any residual lower grade gas or 'pump errors'. This car came from Texas where I believe the premium grade is higher octane than here. That could possibly have something to do with it. Since I put in the 100 octane, it's been running good and I haven't noticed the smell, but I haven't ruled out the possiblity that the cats are going out. I don't have the money for new exhaust right now, but I'm hoping it passes the next smog check... if it doesn't, then I'll do what it takes to fix it. Thank you all for the replies, if you have any more ideas that hit you, bring 'em on!