Mercedes R Klasse Diesel engine issues

The symptoms you describe definitely point towards a potential boost leak in the turbo system. The whistling and hissing noises, coupled with reduced power and increased fuel consumption, are classic signs. A faulty boost pressure sensor could certainly be the culprit, especially if the cable or plug connection is defective, as you suspect. To clarify, does the whistling/hissing sound increase with engine RPM or load? Also, have you visually inspected the hoses and connections associated with the turbocharger and intercooler for any signs of damage, cracks, or looseness? A boost leak will cause the engine to compensate by using more fuel, hence the higher consumption. The jerking could be the engine management system struggling to maintain the correct air-fuel mixture due to incorrect pressure readings from the boost sensor.

Thanks for the quick reply! Yeah, the whistling and hissing get louder the harder I accelerate. I took a quick look at the hoses, but honestly, everything looks like a black snake pit under there! I didn't see anything obvious, but I'm no expert. What exactly is the 'intercooler', and where would I find it to check those connections? Could a simple bad connection on that pressure sensor really cause ALL these problems?

The intercooler is essentially a radiator for the air coming out of the turbocharger, cooling it down before it enters the engine. Cooler air is denser, allowing for more efficient combustion and more power. It's typically located at the front of the engine bay, near the radiator. Follow the large diameter air hoses coming from the turbocharger, and you'll find it. A bad connection on the boost pressure sensor can cause all those issues. The Engine Control Unit (ECU) relies on the sensor's readings to regulate fuel injection and turbocharger boost. If the signal is erratic or missing, the ECU can't properly manage the engine, leading to poor performance, stalling, and increased fuel consumption. Given your description and limited visual inspection, it might be best to have a workshop properly diagnose the turbo system, especially since a boost leak can sometimes be difficult to pinpoint without specialized tools like a smoke tester.

Thanks a million for the advice! Took it to a local shop, and you were spot on – it was the boost pressure sensor connection. They cleaned it up, re-seated the plug, and cleared the code. Runs like a champ again! Total cost was 95€ – way better than I was expecting. I really appreciate you taking the time to explain things.