I have a 2008 R5 (engine code: BPE) and I recently noticed that car getting louder when under load. I've logged some data during a test run, and it seems I have an almost constant difference between the specified and actual MAF sensor readings in engine MVB 003.2 (specified) and MVB 003.3 (actual), with the actual being the lower. I also have essentially the same difference in turbo pressure requested and actual values in MVB 010.2 and MVB 010.3. In both cases the "actual" curvatures don't top out or don't fall to zero, but almost perfectly follow the "specified"/"requested" value - but with a constant ~200 mbar difference.
Now, based on the discrepancy in the MAF readings I'd have theoretized that possibly the MAF sensor is bad. However, because there's a matching difference in turbo pressure readings, it makes me think that there's really a 200 mbar of pressure missing from the system, and the MAF is actually reading the correct actual pressure value.
Am I right with this assumption? If yes, then what could possibly cause a seemingly constant 200 mbar lack of air pressure at essentially any and all speeds/loads?
Or am I wrong, and could a bad MAF reading also somehow caused the actual turbo pressure being lower (possibly because the ECU is working by the specified and not by the actual air mass values, and "underdrives" the turbo because of that)?
Or am I completely misunderstanding the situation here? Any other ideas?
I've obviously checked the air filter and it seems fine. I've no CEL or any fault codes in the engine (not even intermittent ones), it's just that engine is running louder under load than I remember.
Thanks for your help.
MAF log data (light blue - MAF specified, green - MAF actual):
Turbo data (green - turbo pressure requested, yellow - turbo pressure actual):