Background 1996 ES300
373000 MILES
upstream o2 have about 100k Bosch
downstream at least 140k maybe alot more

10 montgs ago after getting a deal at $70 for DENSO fuel pump shipped from denso via autozone i decided to change out orginal fuel pump and keep the orginal as spare in truck. I changed out the all filters on fuel system at that time. YIKES i think the orginal fuel filter was still on car.

anyway about 1000 miles after change out error P0171 started showing up every 1000 miles.

i swapped out MAF sensor with the other 1996 es300 - and still getting code.

looked and looked for vacuum leaks

yesterday after dropping fuel tank to changecout all real lateral rods - i get this p0125 popped up after 10 miles of driving.

since i git a deal at autozone a few months ago on NTK O2 sensor fearing the day the o2 needed to be changed. ( $40 on uppers $45 on downstream shipped from manufacturer)

Fuel mileage is good

so im thinking about changing out all O2 sensors.

am i overlooking something?

 

The whole intake was taken off to change out bypass hose and knock sensor wiring about 35000 miles ago - i cleand out the whole intake system and new PVC valve and valve cover gaskets- WOW was there some carbon build up in there - runs wonderfully now

 

I've only had success with genuine Denso oxygen sensors.

 

mine had the same p0171 error. it ended being faulty A/F sensor. replace with genuine toyota sensor.