if this helps it was a nugget from tribesman regarding injector correction values regarding something in my thread but related to your graph
Injection correction values are only calculated up to around 35mm/inj... Diagnostics show the latest value calculated at lower load, but ECU does not correct the injection at full load...
so basically it looks like as the graph flatlines around 1/3 way across its more than likely that the total fuel injection quantity has passed above the 35mg/I threshold and is substituting values based on just prior.
I tend to think of these values as a balancing function, each injector will inject more or less mg/I than its theoretical ideal based on the acceleration of the crank/piston.
it thinks its too fast it thinks its injecting too much and will reduce accelerates too slow and will inject more ,always trying for a smooth 4 piston strokes also so also balancing across the 4 injectors to achieve a steady smooth rotation of the crank.
so Im still convinced the injectors will sort of mirror each other to some degree, you may have one worse injector (3 or 4 under load) but the opposite injector apposes it to keep smooth so looks like 2 are bad.
yet towards the end of the graph cylinder 1 appears to be the worst.
I have the description of the values here post 194
I would repeat when warm again and just do idle speed 30 secs and then increase to 2000rpm 30 sec and back to idle slowly.
you've tried injector cleaner , I would also be sure to clean the injector plugs with electrical contact cleaner and work the plugs in and out a bit to be sure of a good contact.
then repeat the above idle and 2000rev log see if anything changed.
also bear in mind there is a known weakness In the injector plug/harness for Vauxhalls and seen a few on here in the last few years looking for info on them but I don't remember many posting up any before and after values just issues then issues gone sort of thing.
search for injector number 3 plug and theres a repair kit to solder in.
Diesel - 1.9 JTDm (2) - Autolusso New Alfa Romeo Parts
also bear in mind there could be an underlying mechanical issue affecting the cylinders also like compression rings, valves , leaky swirl flaps leaky egr could all give symtoms the ecu will think is injector variation.
and try a reset leanrned values if it has it, or maybe an ecu reset might help especially after you've done a lot of cleaning of sensors.
also what are values of maf ? a quick log of maf mg/I and boost pressure mbar under a bit of load 3rd or 4th full throttle for second or 2 (due to road conditions and weather)
id like to try to pinpoint stuff before I stuck a £95 injector on it.
that mpg sounds low but the injectors would need to be pumping it in to do it alone does it smoke much ? it would be very rich if dumping in too much fuel , which those values don't look like that bad .
what mpg were you getting before the cold weather, I usually lose around 8-10mpg this sort of weather on winter diesel.