Citroen C5 Engine Issues

Sounds familiar! I had similar symptoms with my old Opel Astra after the spark plugs went bad. Reduced power and a rough idle are definitely signs of a rich mixture. Have you checked the intake manifold or the oxygen sensor? A faulty catalytic converter could also cause this.

Thanks for the insight! I'll look into those. When you say spark plugs, were they visibly fouled, or was it more subtle? I haven't checked them specifically on my C5 yet.

They were pretty black and sooty, which pointed to the rich mixture. But yeah, the symptoms sound really similar to what I experienced before taking it to the workshop. Maybe get it checked out by a pro?

Thanks a lot! After visiting the workshop, you were right. An injector was indeed defective. Replaced it, and the car runs perfectly now. Total cost: 515€.