I have a 2002 Nissan Altima with over 110,000 miles. But I maintain the car well, regular oil changes, gas Et?

That is LOW mileage!! Here is what to do. Buy a can of Gum-out spray, and clean the living dayights out of your throttle body and IDLE AIR CONTROL VALE> When these get dirty, they affect fuel mix. THis affects the O2, This clogs the converter up a little. By running gum-out through your intake system with the engine running, it cleans the piston tops, rings, valve head, and esp the converter and O2 sensor. WHEN YOU ARE DONE WITH THIS< rplecar the plugs with Denso Iridium or BOSCH Fusion plugs. THese burn fuel the best, cleanest, and most completely. You power goes up, and emissions go down. DON'T change the converter until you try my little trick!!