The air/ fuel gauges are only to tell you when you run lean and rich, there a waste really cause they won't correct the problem of a lean/ rich mixture, so it will just tell you the problem is there but, your always going to lean out at certin rpm ranges and richen up on others, you can correct jets and stuff all day but you'd still have a problem, might help it but it would still be there, I think the sensor goes in the exzaust but I'm not shure.