Excursion Reduced Engine Power

It certainly sounds like a potential throttle issue. I once experienced similar symptoms with my older BMW 5-Series; a noticeable response delay and subsequent decrease in fuel efficiency. Has the vehicle entered limp mode at all? I would also examine the air intake and airflow to ensure there are no obstructions contributing to the problem. How does the engine sound at idle?

Limp mode, yes, that happened once. What did you do with your BMW?

Considering the limp mode incident, it strengthens the possibility of a defective accelerator pedal module or electronics within. In my experience with the BMW, the issue was indeed the throttle position sensor. Given the symptoms and the error code, I recommend a visit to a trusted workshop for a diagnostic assessment. It might save you considerable time and potential further complications. Expect around 265€ for the repair.

Thanks for the insights. I'll take it to the workshop as you suggested. They confirmed it was the throttle valve and replaced it.