I have a P0172, and I'm thinking it's an O2 sensor issue. Now would it be one (or both) of the pre-cats? Or would it be one (or both) of the post cat sensors?
Thanks in advance.

 

prodemand / sure trac shows Mass Airflow sensor is the culprit if you need one lemme know i have a 2001 sitting around parts car can hook it up if need it (check fitment first)

 

04 with similar codes as mentioned above P420 P421 these those O2 sensors may be the issue but if it's causing your car to go into limp mode it might be the internals of the "cats" breaking down and causing exhaust blockage. Your car with only go up to 35mph if you know a local mechanic or have the ability all it might take is someone to blow that junk out of them and put them back on it won't clear 02 sensor codes but it will improve your cars performance and get it to where you can drive it again.
the Catalytic Converters in all toyotas were pretty much junk in the early 2000's