Okay, have a 2004Hondaaccord, automatic, 4 cyl. Car has 30k miles on it. Now, I do drive a bit fast sometimes, and have a somewhat heavy foot. But, here lately I've been getting an average of around 21 mpg. Does this sound right? My car had been sitting for a while before I bought it, so I don't know if something is "dirty" like spark plugs or something... ne idea?