Mini Cooper Injection System Issue

That sounds suspiciously like what happened with my old Vauxhall Corsa! Same symptoms: poor performance, rough idling, and guzzling petrol like there's no tomorrow. Have you checked all the basic electrical connections to the injection system components? Any obvious corrosion or loose plugs? What about the wiring harness itself? Are there any OBDII error codes?

Thanks for the quick reply! I'm not very technical, but I had a quick look and couldn't see anything obvious. What exactly should I be looking for in terms of corrosion or loose plugs? And how would I go about checking the wiring harness?

Since you say you're not mechanically inclined, I'd strongly advise against poking around with the wiring harness. You could inadvertently cause more harm than good, potentially bricking the ECU! Given the symptoms and the mileage, and considering that I went through a similar rigmarole, I'd bet on a dodgy connector or chafed wire somewhere in the injection system's loom. I would take it to a reputable shop. They'll have the proper diagnostic tools and know-how to pinpoint the exact fault without causing further damage.

I took my Mini Cooper to the workshop. As suggested, it was a faulty cable connection in the injection system. They cleaned and secured it and it runs like new again. The mechanic said it was affecting the air fuel ratio. Fuel consumption is back to normal, no more smoke, and the engine doesn't stall anymore. Repair cost was 95€. Thanks for your help!