Solved ... looks like it was either the plugs or the fuel injector wiring harness. Starts up like a champ now even in -20C weather.

Sounds like a possible fuel issue - all your P codes indicate a fuelling issue (except P0243) and are likely all related. The fact that it will start when you add a fuel source (cleaner) confirms this, as does your horrible fuel economy. If you're decent with a wrench get yourself a fuel pressure ga...

Is it possible that you have a small exhaust leak? This can sometimes behave like you are describing where it is not noticeable at higher revs but comes back on deceleration. Check around the manifold for black soot stains, use a mirror to look at the bottom side from the top of the engine. The inje...

I think it lasted for like 5 years so not a total fail. Charging system seems to be much happier now. Good luck with the V50!

Code comes back immediately after resetting before driving

I ended up replacing both rear wheel speed sensors as they come as a pair in one harness. The rebuilt unit was a XEMODEX unit and they have a pretty good reputation and warranty so I figured it probably wasn’t a fault in their work. Seems to be pretty good so far, it’s been about a week or so now.