2000 Chevy Impala poor gas mileage

Oxygen Sensor(s), Catalytic converter, EGR valve could be potential problems. If the valve cover is leaking oil you will need to replace the gasket. Do a compression check on the engine just to be sure.

I changed the egr about 6 months ago and that changed nothing. I am in for smog this week. We will see what the readings are. Both o2 sensors are almost impossible to remove.

I am not sure what state you live in but in Texas they keep your inspection fee if you do not pass until you are able to fix the car. If you can not fix it in 30 days...well sorry. Most likely it is your catalytic converter.

Hi I just got back from smog check and all 1-4 are at zero emissions and the other is at 1 or 2 . So things are working properly and yet I still only get 18 mpg. Strange?

Is your transmission in good order? Has the fluid been changed? If not then do so and use a good synthetic. Try a synthetic in your motor oil too as it will add significantly to your gas milage. Use a high detergent gasoline for awhile or purchase some seafoam from the parts store. It will clean out excess carbon deposits from your valve stems, intake manifold and combustion chamber. Follow it as directed.

have you smelled fuel at all, has the engine had a hard start recently. If so it could be a possible fuel pressure regulator starting to leak causing you to use more fuel. also check for small vacuum leaks. this will cause the engine to go lean and use more fuel also