C70 diesel rough idle and poor starting

That does sound familiar! I also drive a C70 with a diesel. Did you notice any misfires or perhaps black smoke? Is it possible the fuel injectors are clogged?

Thank you for your response. I haven't noticed any black smoke, but misfires may be present. Is injector replacement potentially the only solution?

Replacement might not be necessary, but cleaning or recalibration rarely works. I ended up having a defective injection nozzle, causing almost the same problems. I'd recommend a workshop visit, as diagnosis can be tricky.

Thank you. It seems I will take your advice and visit a workshop to have the injection nozzles checked. I appreciate the insight.