2000 Corolla Le Poor Fuel Economy - Toyota Corolla, Chevy Prizm (1998-2008)

So I recently purchase a 2000 Corolla LE Auto with 96k on it and it only gets about 25 MPG which from what I read is on the lower end for a corolla.

The car runs fine and seems to not have any issues at all.

I live in NY and commute about 30+ miles a day highway.

I have been driving it lightly with no heavy foot trying to see if it's my driving and I really doubt it is.

I've also driven a 2009 Corolla with 70k and had no regard for how I was driving and it was getting over 31+ MPG (I know it's a newer car, but I've read all over that older corolla would get better MPG then newer ones).

I also put some fuel injector cleaner in today and unplug the ECU fuse for 30 seconds to reset.

The owner before me provide all receipts from dealer for work done and parts replaced. I was also able to verify the receipts with the dealer to confirm I know overboard but I did.

Here is the list of everything done in the last 10k miles by the previous owner

-Catalytic Converter

-EVAP Canister

-4 New Tires (I've check tire PSI/condition etc.)

-Alignment

-Downstream O2 Sensor

-MAF Sensor

-Power Steering Pump

-V-Ribbed Belt

-Toyota Battery

Any ideas?

I was thinking from reading a lot of post online that maybe the upstream O2 sensor is starting to get sluggish but not pop CEL and considering the previous work done.

A few people say that replacing the upstream sensor has given them back good fuel economy and they had similar issue.

Does anyone know the specs and steps for testing the upstream O2 sensor?

Thanks for any help...

Have to backprobe the upstream sensor, while it is running, to see the waveform. Can also be done via a datalogger on the OBD-II port, but with less resolution. Given the mileage, possible the upstream sensor is cooked, looking at the ST and LT fuel trims will give you more information.

Assume that the plugs are good - doesn't hurt to pull them and give them a good look. OEM ones were spec'd to run up to 120K miles - possible they left the original ones in there. Also keep in mind that winter fuel blends generally get quite a bit poorer fuel economy. Some cases, can hit you for 20-25% less MPG than usual.

Thanks, I was thinking along these lines. Hopefully I can get a nice day on my days off to start testing some stuff.

Have to backprobe the upstream sensor, while it is running, to see the waveform. Can also be done via a datalogger on the OBD-II port, but with less resolution. Given the mileage, possible the upstream sensor is cooked, looking at the ST and LT fuel trims will give you more information.

Assume that the plugs are good - doesn't hurt to pull them and give them a good look. OEM ones were spec'd to run up to 120K miles - possible they left the original ones in there. Also keep in mind that winter fuel blends generally get quite a bit poorer fuel economy. Some cases, can hit you for 20-25% less MPG than usual.