Rifter running rich

I had similar symptoms on my old Volvo V70. Excessively rich mixture can be caused by faulty fuel injectors. Have you checked your air-fuel ratio or inspected the intake manifold for leaks? A defective lambda sensor can also cause a similar issue.

Thanks! I hadn't considered the lambda sensor. Where was it located on your V70 and what were the exact symptoms?

On my V70, the sensor was located before the catalytic converter. I observed increased fuel consumption and black smoke, a telltale sign of incomplete combustion. I would strongly recommend a visit to a workshop to get the car checked, because if the air-fuel ratio is not correct you can seriously damage your engine.

Thanks a lot for the advice! I took it to the workshop. It was indeed a defective injector. Cost me 515€ to get it sorted.