I actually think the reputation of early Bosch FI systems being horrible is pretty overblown. I haven't had a hard time diagnosing L-jet issues (I haven't touched D-jet). It's pretty simple and while you can't plug a scan tool in, you can use an oscilloscope to see what's going wrong. Also it's so simple, there are really only a handful of things to check. Some friends and I do endurance racing in a Fiat with the original L-jet system and it has been reliable.

I can understand a shop not wanting to touch them because you'll likely lose money tracking down issues as opposed to plugging in a scan tool, but for a hobbyist it's really not that hard.

It's also a matter of who integrated it. In the Volvo's they are rock solid because of the way the wiring is routed (and the quality of the wiring), in the DS they are nothing but trouble and you're better off assuming it's all gone and completely rewiring and re-calibrating it than to try to fix it as is because that will almost always be a very temporary job.

That system had a flap in an air passage that metered air flow. If the car backfired, the flap could change position relative to the indication that went to the control unit and that threw off the air/fuel mixture. They were also more sensitive to air leaks than a carbureted car.