Mini Cabrio Faulty Injection System

I had a similar issue with my Mini, though it's a Diesel. Experienced comparable symptoms: higher fuel consumption, a noticeable drop in engine performance, and occasional stalling at idle. Have you inspected the cable connections and plugs related to the injection system? A loose or corroded connection can definitely cause those problems. Start there; it might save you a trip to the workshop.

When you mention cable connections, are you referring specifically to the injector wiring harness or other related sensors? Also, did you observe any smoke during acceleration, similar to what I am experiencing with my petrol Mini Cabrio?

Yes, I was referring specifically to the injector wiring harness and connections to related sensors within the injection system. I did not observe smoke, but each engine can behave differently when facing the same problem. Given your observation of smoke, it would be wise to have a professional check for any potential fuel leaks as well. It is possible that a faulty connection is causing an improper fuel mixture, hence the smoke. Given the potential complexity, consider a workshop visit to diagnose it properly. Do not attempt to drive it too much until fixed.

Following your advice, I checked the cable connections, and you were spot on. A visit to the workshop and 95€ later, the defective plug connection on the injection system has been resolved. The engine is running smoothly again. Many thanks for your assistance.