Volvo S90 Defective Injector

I had similar symptoms with my S90. Have you checked the intake manifold or the catalytic converter? A rich mixture can damage the catalytic converter.

Thanks for your reply. No, I haven't checked those yet. I'm not very experienced with car repairs. Is there an easy way to check the intake manifold or catalytic converter myself? Or should I check the spark plugs?

It sounds like the same issue I had – a faulty injector. While you could check those things, diagnosing injector issues usually requires specialized tools. I'd recommend taking it to a workshop to confirm. They can properly diagnose it.

Okay, I understand. Thanks for the advice. I took it to the workshop and they confirmed it was indeed a defective injector. The repair cost me 515€. Appreciate the help!