S90 rough engine reset quantity drift compensation

Interesting. Have you done any diagnostics besides reading the error code? Like checked fuel pressure or injector performance data? The 'reset quantity drift compensation' error can be from fueling issues, not always a bad injector. A faulty high-pressure pump can cause this. Knowing the exact error code would help.

Thanks. I haven't checked fuel pressure or injector data, just read error code P0203. Could a software refresh fix this, or is hardware replacement more likely?

P0203 points to an injector circuit malfunction, and software rarely fixes hardware problems. Resetting the adaptation values might temporarily improve it, but the underlying injector issue will likely persist. Given the symptoms and error code, a faulty injector is most likely. Have the injectors professionally tested. Replacing the injector is probable. Go to a trusted workshop. They can assist you further. Final repair costs were around 515€ in my experience.

I appreciate your input. A workshop visit is the most sensible thing to do. Thanks for confirming my suspicions about the injector. I will book an appointment and have them diagnose the issue thoroughly. The final bill was very similar in my case.