Lean on both banks not O2 sensors
 

Lesson learned, the Mpv was throwing lean both banks all of a sudden. Just after filling the fuel tank. Thinking we got some bad gas I loaded up the tank with gas drier. Still ran crappy and now a check engine light. I work on late model diesel trucks for a living. I have not had to do much gas drivability for many years. The car ran well at full throttle so I knew the pump and filter were fine. I borrowed my Snap-on red brick from the car lot I loaned it to 11 years ago. The O2 sensors read 0.02 volts until I got way into the throttle then they would sweep like they should for a while then settle back to nothing. I ordered 2 Denso sensors from Rock Auto and installed them..... Crap no change.
So I read a little more on line and saw about the pcv hose issues. So I checked out the hoses and they seemed fine. Read a little more and someone mentioned a dirty MAF sensor. I was getting what I thought were good readings for it, but might as well check it out. I unplugged the MAF and the O2 sensors went full rich. We are on to something, this car disregards O2 when there is a problem with mass air flow. I removed the MAF sensor and there was a very small blade of dry grass across the hot wire.
Now the O2 sensors sweep at idle and down the road, it will have to relearn all the fuel trim again. My daughter is glad to have her minivan back again.
Maybe this is a Mazda thing with the MAF priority over the O2 thing, I have not run into that with Fords or GM.
Hope this helps someone before you buy O2 sensors. They don't cost much but they sure are fun to change even with a hoist.
Andy

My mazda mpv 2000 also giving me a headache as it’s petrol consumption is very extremely high. It’s ridiculously running at 2.5km/L status !!!

I had order MAF and an extra O2 sensors to change once it arrive from overseas and will see how it performs.

Wondering how’s your fuel consumption like?

One thing… how do you know if the vehicle is running full rich / lean?? How to know or test?

I have a diagnostic scanner, not just a code reader. I had a repair garage for years and repair trucks for a electric utility now. Fuel use is about 8.5 km/l on the highway.