oxygen sensor on 1998 Toyota 4Runner

where is the oxygen sensor located and how hard is it to replace?

Asked by for the 1998 Toyota 4Runner
there are upstream and downstream o2 sensors. you need to know which one specifically is bad.
did you get a real diag or a free code pull. if you got the code pull, have the diag before you replace it. a code never identifies a bad part just a failed system.
what code did you have??

I put a k&n air filter on it and now I am getting 50miles per 1/4 tank of gas. That is horrible, I know the oxygen sensor will cause extreme gas intake and thought it might be the reason.. I haven't had the sensor tested yet. If you have any other reasons for this I would be very grateful.
get rid of the k and n filter. it contains oil in the filter and that contaminates the sensors. i would start there before doing anything else.

Thank you so much, I'll do that!
good luck