You've got it a little backwards. Starving an engine of air forces a rich mix. If all else remains the same, the CAI will add more air, thus leaning the mixture out. However, if the ECU is trying to hit a A/F ratio number (I've seen the MS3 at around 9:1, which is pig rich), it will just add more fuel. I do have a feeling, however, that Mazda designed the ECU programming to accept a certain amount of extra air at the same throttle position (this is where an electronic throttle comes in handy). If it were a mechanical throttle, the ECU most certainly would throw more gas at it immediately. This jives with the reports that people who have installed the CAI have had an increase in gas mileage. It means the engine isn't using more fuel to create the extra power. It's probably running closer to 11:1. Still, ideal AFR for gasoline is 14.7:1. Not the safest bet, however. I wouldn't lean a turbo much past 12:1 however. If you don't want to turn the turbo into a block of molten metal, you'll always be lean, and always eventually have a black tailpipe.
