Well, the mustang's been running just fine since pulling the Steeda underdrive pulleys a couple weeks ago. They were adjusted and examined by several parties, and even the dealer's mechanic couldn't see anything wrong with them since the correct bolt was installed, nor could he diagnose exactly why the car was throwing SES codes. Either I got bad pulleys or my mustang just doesn't like them. In either event, I'll have to look for other ways to improve RWHP. Anyone want to buy a C&L MAF kit or Steeda underdrive pulleys for a 2002 Mustang GT with less than a couple hundred miles on them? Perhaps you'll have better luck with them than I did! I doubt there's anything wrong with the MAF kit, but after this expensive little trip down "bolt on" horsepower lane, I can't say as I'd recommend the pulleys to anyone despite having a good reputation and many successful testimonials. They just didn't work for me!