VOL FCR and questions Volvo 960 smokes, rough idle erratic

[Noerty]

Hello Community,

I have been driving a Volvo 960 in South Africa for 2 years now. I am struggling to pinpoint to a problem my car developed recently. It smokes when it is hot about 100 degrees C fluid temperature more like blue smoke. Also it sometimes idles rough when it is warm at about 80 degrees C fluid and up. When it has the rough idle it is clearly present that it smokes black.

I checked the ignition coils if one of them is not faulty (pulled the injector plugs one by one). No specific cylinders is affected. Also checked spark plugs they all look like the car is running too rich.

I organised the Vol FCR software because I figured that might help to diagnose the problem. I cleared codes and drove, the problem occurred but no new codes present. Then I checked life data to see if O2 sensor works. I only get -0.175V at all times. Nothing changes there. Is my O2 sensor faulty? I put the setting to Front and Rear O2 sensor signal. Both show the same value.

Other than that I couldn't really see anything weird looking at live data.
I also pulled the oil dipstick to see if my PCV system is fine but no smoke coming out of the dipstick. Is that a reliable method to check? Also checked no bubbling in the coolant wanter, no white deposits in engine oil.

Do you guys have any other idea what I should check? About 1 year ago I had to replace the intake manifold gasket and cleaned the PCV system as much as I could at the time... I don't really feel like taking everything off once I haven't checked other options.

I would greatly appreciate your help!