Barnabas

Hello guys,

Ever since I bought my car (2003 ES300) it has been giving me really bad MPG, 10-14 AVG MPG City and 17-19 AVG MPG Highway. So, as I was fixing things here and there I didn't want to go there yet but the time has come and after some research, I will be changing spark plugs, Air Flow Sensor (already changed the air filter) and I also want to change the air fuel sensor or oxygen sensor in charge of that area of the vehicle. I looked but couldn't find a clear answer. Since you guys are the expert I would love for some help.

Here are the parts number for each Sensor. So Which one should I change? or should I change them all?

Position: Downstream Front

Position: Downstream Rear

Position: Upstream Rear

Position: Upstream Front

Edit: Year and model of the car

Oro

1) What car do you have (hate to ask, such a fundamental question)?
2) What CEL codes were throne?

Asking the questions you are asking, it sounds CEL-driven.

Barnabas

My car is a 2003 ES 300. There is no code yet, I am changing it based on the suspicios that it might be the reason why its giving me such a low MPG, I am going to change the spark plugs first before I do any of that to start from there.
I am changing it based on what my mechanic told me and also based on things I've read in this forum during the past few days about the subject.

fortitude

There are other components that could lead to poor gas mileage. A mechanic who has diagnosed & CONFIRMED a part being faulty should be able to readily reference engine data such as fuel trims, AF/O2 volts& wave patterns, even ohm resistance figures against factory specs. Given the poor MPG you have, it requires a thorough review of these data points, soon.... If the fuel system is loading the engine with too much fuel, it will eventually destroy your catalytic converters.

Barnabas

Guys I truly appreciate the help! But the problem is tht in every post about low MPG everyone suggest "Change O2 sensor" or "Change AF Sensor" even if its not throwing a code. I ask which codes and don't get the answers I'm looking for.

This may sound expensive in case they work fine, if changing these things don't help I will take it to the dealership. I just want to do some exploration of my own based on other's experiences in this very same forum.

Thanks again for your help!