Citroen C1 engine light rough running exhaust smell

Sounds frustrating! I had something similar happen with my old 2012 Renault Clio, though it was a diesel. Engine light, rough running... turned out to be a dodgy lambda sensor messing with the exhaust treatment. Have you checked that? Could also be EGR valve related, or even a particulate filter issue if it was diesel.

Lambda sensor, eh? That's a new one for me. How did you figure that out? And what exactly does that sensor do?

Well, the garage diagnosed it, to be honest. The lambda sensor measures the oxygen levels in the exhaust and sends that data to the engine management system. If it's faulty, the system doesn't know how to properly control the fuel mixture, causing all sorts of problems with the catalytic converter and exhaust. I'd suggest getting yours checked out, could save you a lot of headache!

Thanks a million! I took it to a garage, you were spot on! Lambda sensor was indeed the culprit, plus a small exhaust leak. Cost me 375€ to fix everything. Engine's running smooth as butter now!