Sudden drop in Mileage

I have a 2002 cavalier 4 door automatic that up until three weeks ago was getting between 26 and 30 mpg. Now all of a sudden its only getting 15 mpg. There are no codes or any other symptoms just bad mileage. Anyone ever heard of this before?

I have a 2002 cavalier 4 door automatic that up until three weeks ago was getting between 26 and 30 mpg. Now all of a sudden its only getting 15 mpg. There are no codes or any other symptoms just bad mileage. Anyone ever heard of this before?


You can try changing the oxygen sensor, the one before the cat, if that does not work, try professional fuel injector cleaning.

its probably a combination of reformulated gas and the cooler weather(poorer fuel atomization which is also due to winter gas). mine dropped from 30 to about 20 but as soon as it gets warmer and the summer gas comes back itll shoot right back up to 30.