My neon has 64k miles on it. I was getting about 30mpg. Now 21. I tried replacing o2 sensor but it threw same code. Under that code it list a multitude of things it could be. What I don't understand is if it's o2 it should throw that code. If it's a map sensor it should throw that code right. Why is it giving me such a generic code. Vacuum? I dont hear any leaks. Plugged cat? Doesn't idle rough. Any suggestions