has anyone changed out the air filter from the stock to more performance one and how that effects the car sensors. I'm talking aobut the round one that racers use. I'm thinking if I change over, maybe an increase in gAS MILAGE or performance. Any advice. I have a 99 Deville concour. I just love the ride and power.

yea dude, get a K&n air filter or something made of the same gauze-High flow material, they are great! they increase horsepower,torque, throttle response and increase gas mileage!