I have an 03 Impala with the 3.8 V6.
The car has about 60,000 miles.
We normally got about 30 mpg on the highway and now it is about 22.
We use fuel injection cleaner and the mileage improves to about 26 for 2 or 3 fill ups then returns to about 22.
I do not want to put it on a steady diet of injection cleaner.
What can cause the problem?

 

Well at least you get better fuel mileage then me. I have a 01 impala 3.4 with 118,000 miles and im only getting about 14mpg. I just bought the care not to long ago so I dont know what kind of mpg im suppose to be getting. Im thinking about getting a new fuel filter to see if that is some of the problem. Otherwise I dont know what to do.

 

Thanks for the input and so sorry about your lousy mileage. I have already changed the fuel filter with not improvement.

I have no check engine lights and it runs well, it just isn't getting the mileage it once did. With gas prices on the rise again mileage is important.

 

My 03 is averaging close to the same as yours. I just bought the car a week ago and it has 110k on the oometer. I am guessing right now, but my bet is going to be3 on tune up min plugs and wires. I will let you kow what my outcome is.