Gas Mileage Stinks on 2004 Chevrolet Malibu Maxx

I use to get 30 miles per gallon on the highway. I'm lucky if I can get 21 now. I have maintained the vehicle on a regular maintenance schedule, but at a loss as to why it sucks now. Car sometimes has a "lag" and seems like it wants to die when idling, but dealership couldn't pinpoint anything. Any suggestions?

by in Kent, WA on March 21, 2011
3 answers
ANSWER by on March 21, 2011
Do you have any check engine lights? The probs you are experiencing are typical if starting to have oxygen sensor probs. Have a tech attach test equipment and monitor response times of the O2 sensors.
ANSWER by on March 22, 2011
Whomever you have connect to the car' computer will be able to look at short term and long term fuel trims to determine whether or not the computer has been enriching the fuel mixture.
ANSWER by on March 22, 2011
Whomever you have connect to the car' computer will be able to look at short term and long term fuel trims to determine whether or not the computer has been enriching the fuel mixture.