Car engine runs smooth but gas mileage suddenly is 5 mpg less

Anything that sudden, probably requires a call to your mechanic for a checkup.....

Is the check engine light on? If so get the ECU scanned for codes at a local auto parts store and post the codes here. A bad O2 sensor can do this, but it will usually illuminate the check engine light.

GAS MILEAGE BAD WHY SUDRNLY

Just went through this with my Lincoln Town Car. When was the last time you changed the fuel filter?

Hey guys why does my 1997 suddenly have decreasing mileage. Lost about 4 miles per gallon past month. I had the maf sensor cleaned (mechanic used alcohol) and plugs and wires changed. Should I have fuel filter changed? Also, no engine light but temperature sensor is possibly bad. I assume mechanic meant fuel sensor. What should I do first and what priority??? . I can't spend more money but will to fix if possible!! 200 or less God willing... Help me pls bros, a sister in need.. june

I got additional 3 MPG by just changing the fuel filter. Please keep in mind, to the simple things first - Spark plugs, fuel filter and air filter.