I've been getting pretty bad gas mileage for a lil while now. The best I have done on like a full tank of gas is about 240 miles before I had to fill up again. This doesn't seem right to me at all. I was thinking about getting a tune up done to see if it cleared it up but would a need of a tune up really cause this bad a mileage? Is there anything else that could be causing the bad mileage? I remember hearing someone say that the pcv valve being bad could cause that? Any suggestions? Thx in advance!