C30 Reset Quantity Drift Compensation Error

That 'reset quantity drift compensation' error on your Volvo C30 definitely points towards the fuel injection system, specifically an injector problem. Have you checked the injector values using onboard diagnostics? Sometimes you can pinpoint which cylinder is causing the issue that way. It could also be worth checking the airflow sensors, but that's less likely given the specific error code. What sort of performance tuning, if any, have you done to the car?

I haven't checked the individual injector values, to be honest. Where would I find those via onboard diagnostics? I haven't done any performance tuning, it's all factory settings.

Okay, factory settings make things a bit simpler. You should be able to access the injector values through the engine control unit (ECU) using a diagnostic tool. It varies a bit depending on the specific tool, but look for 'live data' or 'real-time data' related to fuel injection. See if one injector is way out of range compared to the others. Honestly, though, with that error code and the symptoms you're describing, it's probably best to get it checked by a workshop. A defective injection valve/injector is the likely culprit, and they'll have the proper equipment to diagnose and replace it correctly.

Thanks for the advice. I took it to the workshop, and you were right – a defective injector was the issue. New injector fitted, and the error is gone. Cost me 515€, but the car is running smoothly again.