My car is eating more gas than normal, what should I check?

Question

I have a 2003 infiniti g35 sedan and i noticed that its mpg has decreased from 20mpg to about 15mpg. Is there anything I can check or change, like some filter or fluid, on my own to see an improvement in this number?

Answer 1

Something is broke. That is why your check engine light is on.  That's right, it is on and I know it.  There is a definite correlation to the light and the poor mileage.  You should fix it before you clog $1500 worth of catalytic converters (it has four).

Answer 2

Air filter, tire pressure, fuel filter, your driving style.

Answer 3

air cleaner !

Answer 4

You engine could be running 'richer' on fuel due to a lack of oxygen or valves staying open longer.  A few things to check.

1. Air filter, check for dirt and proper air flow

2. O2 Sensors are bad - they go sometimes.  They regulate air intake.

3. Valve dirt, you may be running on dirty gas.  Try a valve cleaner and use gasoline with cleaners in it.