R Klasse Diesel Intake Manifold Flap Control Problem

I had similar symptoms with my R Klasse diesel: loss of power and rough running. Check the intake system thoroughly, especially the intake manifold itself and the flap control mechanism. It could be a defective switch. I had an engine misfire issue as well at the time.

Thanks for the quick response. When you say 'defective switch', are you referring to the actuator that controls the flaps in the intake manifold? Was the engine performance noticeably affected?

Yes, the actuator. The engine performance was definitely down. I recall a similar hissing sound too. I'd suggest getting it checked by someone who knows these engines well. It may save time and money diagnosing it yourself. My issue ended up being more complex than initially thought, but it all started with similar symptoms.

I took your advice and got it checked out. It was indeed the intake manifold flap control, as suspected. Repair cost 465€. Runs like new now. Thanks for pointing me in the right direction.