'97 Elantra - Low MPG

I have a '97 Elantra Wagon with about 60,000 miles. I had been getting low
gas mileage (19 to 20) for a while. I had some muffler work done at which
time I discovered that the exhaust manifold was cracked. I had that repaired
and assumed that was the cause of the low mpg.

Surprisingly, the mpg has not changed. It's still around 20. Now I know
that the EPA estimate which is usually a little high is 27/32. Any ideas
about this from anyone would be appreciated

 

What gas mileage did you get earlier on, and how are you measuring the gas mileage? Have you taken a freeway trip and checked the mileage in sustained high gear (a lot more consistent then city driving)? Did you check the air filter, tire condition and pressure?

 

If it were the oxygen sensor, your check engine light would come on, I
think.

http://auto.howstuffworks.com/framed.htm?parent=question257.htm&url=http://www.forparts.com/o-21.htm