PNM35 running very rich, rough idle, limp mode and so on

[Hertz Donut]

I know, I searched, which is pointing towards what I suspect but I need validation. Validate me, folks, please.

After all these years my Stag (VQ35DE) has now been relegated to farm hack and general waste carrier. It's performed near-faultlessly, and is a well-loved, albeit neglected, part of the collection. Then a couple of months ago or so the exhaust rusted through, with the rear muffler left hanging by the rubber. It was loud af but hilarious to drive around in while I waited for an exhaust shop appointment a few days later. I live in a rural area so not too many people around to annoy.

Then after a while on the beans it suddenly dropped into limp mode with a CEL. No worries I thought, I'll sort it after the exhaust is fixed. Got the shop to clear the CEL and away we went, sweet as a nut.

A few days later it went into limp mode again. I gave up and took it into my local Nissan dealer to get it diagnosed. They're possibly the worst dealer in all of humanity and said the air filter was blocked, we tapped it out and cleared the CEL, here's your several-hundred-dollar bill. I swore twice - once at them, and once to never return to them.

Naturally a couple of days after that the CEL was back on. Fuel smell in the car, stalling when engaging D after a cold start, unsteady idle when cold, in and out of limp mode, CEL, the whole works. Left-side exhaust tip (standard dual tip muffler) is black.

SO...

I'm guessing most likely candidate is O2 sensor, otherwise airflow sensor? The latter was replaced a few years ago (unnecessarily) but I guess it could have failed. I have an OBDII scanner but it's not good enough to find out exactly what the issue is - it says the AFR is 16384 (i.e. high values) and can't detect the fault code, although it will clear the CEL.

if I pull the O2 sensor out can I test it somehow? Run a current through it and check for a reading? I've never had to deal with this side of an engine before.

As I say, this is now a farm hack that spends most of its time being driven into garden walls and paddock ditches by my son so I'd rather not throw a bunch of money at it, but best guess backyard mechanic suggestions will be gratefully accepted.

Cheers.

Edited November 2, 2021 by Hertz Donut

[Hertz Donut]

For those playing along at home, I took a punt and replaced the AFM (realised I'd bought a replacement years ago but never fitted it), and it's back to normal now. Then a couple of days ago the rear view mirror fell off on a heavily rutted road. Sigh.

Edited March 13, 2022 by Hertz Donut