Mini Cabrio check engine light and exhaust issues

Sounds familiar. I had similar symptoms a check engine light, rough idle, and a strong exhaust smell with my old sedan. It turned out to be a faulty EGR valve messing everything up. Do you notice any difference when the engine is cold versus warm? Have you checked for any obvious cracks or leaks in the exhaust pipe between the catalytic converter and the engine?

EGR valve issues with a gasoline engine? Isn't that more common on diesels? And no, I haven't visually inspected the exhaust pipe yet. Where exactly should I be looking for cracks?

Yes, my bad, was thinking of the NOx sensors since you mentioned those. Sorry for the confusion. Regarding the exhaust pipe, check around any joints or welds, especially near the catalytic converter. Honestly, though, with those symptoms and mileage, it's probably best to get it checked by a workshop. They can test the oxygen sensor properly.

It was a defective oxygen sensor, like you thought. I replaced it, and the check engine light is off, no more rough running or exhaust smell. Cost me 375€. Thanks for the help.