Hi,
I used to get 17 - 19 mpg local and 25 - 29 mpg on highway with my 1996 volvo 850. I was very happy with that considering many problems brickboarders have suffered.
After my car hit 120,000 miles, a couple of check engine lights have turned on. First it turned out to be aif flow mass. My mechanic didn't do anything and the light disappeared once he reconnected the battery. I didn't see any significant change in mileage at that time. Second was rear oxygen sensor. While I drove the volvo with the light on, I noticed that highway mileage dropped to 20 or so, which never happened before. A mechanic asked me whether I noticed a change in my mileage and I said yes. I was told that I will get my usually mileage back once the oxygen sensor was replaced. I, though, didn't see any significant improvement yet. Well, I have to admit that I didn't do anything special such as fuel injection cleaning, replacing plug, wire, etc. for the last 5 years or so. I did it when I bought the car with the mileage of 70,000 back in 2001. That was the last time. I though changed air filter and oil filter regularly and kept the tire at the right pressure and so forth. Any suggestions I might try to get my mileage back would be greatly appreciated. Thanks.