V90 Boost Issues

From your description, a defect within the boost pressure system is highly probable. The symptoms you've detailed – reduced engine power, poor engine response, elevated fuel consumption, stalling, and the presence of unusual noises such as whistling or hissing – strongly suggest a compromise in the turbocharger's efficiency. The check engine light further substantiates this concern. Have you inspected the MAP sensor or the throttle body for any anomalies or obstructions? Furthermore, could you provide more detail regarding the conditions under which the whistling and hissing noises are most pronounced?

MAP sensor looks okay. Throttle body seems fine too. The whistling is constant above 2000 RPM, and the hissing is definitely loudest under heavy acceleration. Does that help narrow it down?

Based on the supplementary information, particularly the consistent whistling above 2000 RPM and the prominent hissing during acceleration, a failure within the wastegate valve mechanism is a strong possibility. This valve is integral to regulating boost pressure, and a defect can manifest in the symptoms you are observing. While a DIY inspection is possible, I would recommend consulting a qualified technician for a comprehensive diagnosis, including a pressure test of the turbocharger system. Be prepared for potential repair costs; a wastegate valve replacement, if required, can be in the neighborhood of 860€.

Thanks for the detailed insight. I appreciate the confirmation. Dropped it off at the shop; wastegate valve it is. Costing me about what you said.