Gas Mileage Down

Hi,

My wife has a 94 Olds Cutlass Supreme SL 3.1L. Her gas mileage seem to be getting worse. This last tank she got 24MPG!

Wondering what are some good things to check? Is there a way to pull codes? If so, a resource to tell me what the codes mean?

The plugs are new and the air filter is new.

Thanks
Scott

I found a link to http://w-body.com/index2.html which shows me how to pull the codes.