My car is getting bad gas mileage what should I do?I have already replaced theair filter, fuel filter, and got this stuff from autozone that cleans the fuel injectors but i have to put it in with a full tank of gas. Thanx in advance.

 

New spark plugs. Maybe wires.

 

O2 sensor, tires inflated properly, brakes rubbing...

 

do a seafoam maybe. heres a link i found to show how to do it.
http://www2.ls1tech.com/forums/showthread.php?t=534376

 

so if my rotors are sqeaking that could give me bad gas mileage?

 

no, you have to do your front breaks lol.

 

is it hard to replace the O2 sensors? How can you tell if they are bad ? If i replace the spark plugs which brand would give me better performance ?

 

well...if the brakes are rubbing, then the car doesn't accelerate and cruise as easily, therefore you have to give it more gas...so it can affect the mpg a little...

NGK and ACDelco spark plugs are good...

O2 sensor is easy...I'd stay away from autozone cheapo brands, I'd get AC Delco parts

 

Bosch platnium + 4's are great plugs, you'll see a difference.

 

If the MIL lite is lit you need to take of that problem first. Otherwise go for a new set of plugs and wires. Misfires, dirty air filters,and bad O2 sensors are the main cause of poor mileage in computer controlled cars.
The O2 sensor has a great bearing on fuel economy. They are easy to change out, about the same as changing a spark plug, except thatyou need a sensor socket to avoid twisting the wires off.They can only be tested by using a scan tool and observing the frequency of the voltage change. Slow or nor changes=lazy sensor=poor fuel mileage. I recommend you stay away from Bosch sensors. Get Delco or Denso.