Mini One Diesel Throttle Valve Issue

High fuel consumption and poor starting could be a number of things. Have you checked the air intake for any obstructions? Also, when was the last time you performed throttle cleaning, paying close attention to the throttle body and engine throttle's control valve?

The air intake seems fine. I haven't done any throttle cleaning recently. Could a defective accelerator pedal module really cause these issues even if the throttle body itself appears clean? How does it connect to the engine throttle?

If the accelerator pedal module is faulty, it can send incorrect signals to the engine control unit, affecting the air-fuel mixture and causing both high fuel consumption and starting problems. It's connected electronically, controlling the engine throttle indirectly. Given your symptoms and the age of the vehicle, it's plausible. Probably best to get it checked at a workshop to confirm the diagnosis though.

Just wanted to update this thread. It was indeed the accelerator pedal module. The repair set me back 205€. Fuel consumption seems back to normal now. Thanks for pointing me in the right direction.