I was working on my son's 19TZi, which had been running badly. Matters would improve somewhat if injector cleaner and an "Italian Decoke" were used!

We therefore pulled the injector nozzles out and what a shock we got!!! The nozzles were buried in a pile of carbon. How it went was an absolute mystery. Looking down the hole the nozzle fits into, which is about 12mm diameter, there was only a hole of about 4mm wide that was where the nozzle actually sat in there, buried in this pile of carbon, and was obviously 'dribbling' rather than 'injecting' the fuel into the cylinders.
Once we had pulled the injector nozzles out, I fitted a set of "O" rings, washers, end caps and filters to each one. They come in a set of two made by a company called "ACA engine management solutions" part number IRK711, these came at a cost of $11.55 a set, so for around $23 and an hour of your time, you can totally redo the injectors in your
BX. If however you have a 16V you'll need to invest an extra 55 cents for a 9th "O" ring for the fuel rail.
Waiting to now get it all back together to see how much difference it makes to both performance and fuel consumption.

Anyone with any sort of injected BX is advised to remove their injectors, check for carbon build up, and fit new seals to the injectors!