Volvo C70: Engine Misfire at Low RPM

Hello everyone.

We have a Volvo C70 here with the D5244T8 5-cylinder diesel engine, and it's giving us a lot of trouble.

It stutters at low RPMs, but once it reaches a certain RPM range, it runs completely normally and pulls smoothly.

Quite a few things have already been tried, and the following parts have been replaced.

Injectors, EGR valve, crankshaft sensor, fuel filter.

The injectors were calibrated at the Volvo dealership, and the idle stabilization system was also checked.

In addition, the valve timing was checked multiple times.

So far, all attempts have been in vain.

The crankcase ventilation system generates relatively high pressure, which is easily noticeable by the gases escaping from the "oil separator." If you pinch off this hose, you can clearly feel the pressure building up.

The engine has now been disassembled, and the cylinder head was sent to an engine specialist to be checked for any cracks, but unfortunately, the results were negative.

The symptom of the engine misfire suggests that the engine is firing randomly. We also replaced the fuel during the fuel filter change.

We're slowly but surely running out of ideas, and I hope someone can help us.

Hi,
It's a diesel engine, so it can't ignite spontaneously. I also assume it's a common rail diesel engine.
What is the rail pressure like, specifically within the problematic RPM range? In a VW CR diesel engine, the CR pressure is regulated by two valves depending on the load.
Has compression already been checked?
hg
Herbert.