Really Poor Gas Mileage on 2001 Volkswagen Jetta

I have 141,000 miles on my Jetta Wagon and on my last road trip I only got 18 mpg per tank. I have replaced my MAF and I have new spark plugs and a new air filter. Does any one have any ideas. I'm thinking I might need to replace my o2 sensor but just curious if anyone knows what might cause this. I absolutly love my car and have zero other issues. Thanks for the help.

by in Billings, MT on February 22, 2010
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1 answer
ANSWER by , February 22, 2010
I wonder if looking at fuel trim figures on a scan tool would show up anything. If the O2 sensor was falsely reading lean the computer would richen up the fuel mixture. Air flow sensor would also cause poor gas mileage if were sending a false signal. A vacuum leak could also result in the computer richening up the fuel mixture.