I have a 02 honda accord 2.3 4 cyl and i have been noticing decline in mpgs?
 

the car has the potential to average 25 miles per gallon, but recently it's been averaging 19 which is terrible for that model of car. I'm thinking it could be the air filter , any other ideas?

Was it built in the USA? Try trading it for a car made in the USA, they are made to run on American fuel.

Your honda should even get better than 25 mpg../we gave one and it gets 30 to 35. My suggestion is.. new air filter, tune-up and oil change and have your cat. converter checked to see if it isn't getting plugged. I dont know where you live and sometimes cold weather plays a part in your mileage esp. if you let your car warm up for a long period of time.