I am assuming no4 is still working as the car will still run, sometimes very well other times like a twenty year old lorry.
You mentioned the power steering in last post, would it be possible that low fluid levels could cause the cutting out as it generally happens when changing down gear with foot on brake negotiating a bend in the road before needing to stop for a junction. If the diesel has no lambda in the cat as I have not even looked I just assumed as for age of car I would have said it was breather problem just like the good old festas/orions that people hadn't put the red pipping back on the cab's if I remember right.
Or is what I just wrote the symptomes/tell tale signs of this fault 82.
As I killed the battery this morning and couldn't find a suitable replacement I obviously haven't tried to do umpteen clean starts to see if the fuel out of range is due to insufficient life in the now dead, in every meaning of the word, battery.