Ive decided not to Turbo or swap my 99 2.5 RS Impreza. I simply want to experiment with bolt ons and things like that. but this question is about electronics, but i'll start with my questions about A/F Ratio 1. I want to buy an air fuel ratio guage and im assuming running perfect (or as close to ) is best for power. 2. How can a cars a/f ratio be thrown off? When I get say a CAI, and Headers and a cat back, will my stock a/f ratio be different? or can it be? 3. Do stock engines A/F ratio get thrown off over time?