Bad gas mileage

Hello everybody,
I have a 2008 Cobalt 2 door coupe, I bought the car about six months ago, lately my gas mileage has been terrible, I am getting 20 miles per gallon the most whether its highway or local driving. My driving habits are very easy, no A/C on and no heavy load. My tires are filled up a few pounds over the recommended tire pressure and I keep up with my oil changes. Any suggestions would be helpful before I go to the dealer.

Thanks!

No check engine light?

Sounds like something has tripped up OPEN LOOP mode, which is cold start operation / MAX fuel delivery to motor.

Yeah, my guess is open loop on an injector. Same thing happened to my friend's Redline. Does it misfire at all? If so, I will bet that this is the case.

Check your spark plug gaps too, set the to .32 or somewhere around there.

See if you can get a hold of a set of injectors and swap them out, see if that works. You can probably have the dealership do this.

a bad front 02 sensor with cause it and not give a code.