My gas mileage has dropped to under 20 mpg. I have changed the plugs, air cleaner, and put fuel injector cleaner in. The car runs good, idles good, starts good. I have put a new oxygen sensor in. No check engine codes come up when you plug it into the computer. Does anybody have any idea why I am getting such poor gas mileage?

 

do you just have the one sensor? you might need to replace both sensors, don't use bosch ones or bosch plugs either hope that might have been helpfull

 

I changed the bottom oxygen sensor (it may be a Bosch). I never changed the top one. I'm using Champion plugs.
What's wrong with Bosch?

 

Bosch is ****, plain and simple on the Neon, for some reason nothing Bosch makes for the Neon works, change both your oxygen sensors and maby change your oil. Also Make shure you have plenty of air in your tires. Use copper plugs and wires, platnum is garbage on the Neon, cheap motor= cheap plugs. Its the song and dance of the Neon world.

 

yeah bosch makes nothing the that has a positive outcome for the neon, your upstream 02 sensor is the main one, really important helps with the fuel ratio so your car knows when to adjust, as for the downstream that just checks to see if your cat is working correctly, so basically do what highline has said do a tune up. new 02 sensors, change oil, new oil filter, clean air filter( I have a K&N one reusable and helps with gas mileage) new plugs and new wires, and correct tire pis for the neon i think its 40, well thats what I put mine at. so in conlusion do a tune up and you should notice the gas mileage come back some.

 

could be a clogged cat

 

my two cents... a cloged cat look good to be!! have you tried suprem fuel insted of ordinary.... i drive mine with suprem fuel(sometime ethanol, once a month, clean the combustion chamber and the intake manifold too) i can do Montreal-saguenay(if not familiary about Quebec.. i'm sorry it's 1100 km go'n'back) with only 2 tanks.... try it !!