Peugeot 207 diesel power loss smoke

Sounds familiar. I had similar symptoms with my old Opel Corsa, a petrol one though. Reduced power, check engine light... It was like trying to run with a blocked nose. In my case, it turned out to be a vacuum leak messing with the engine's air-fuel mixture. Does the Peugeot use similar emissions test/recirculation?

Interesting, I hadn't considered a vacuum leak. I'm not very familiar with diesel engines, but would a vacuum leak cause all those symptoms, especially the smoke and hissing? How did you diagnose the vacuum leak on your Corsa?

Well, the smoke could be from unburnt fuel due to the engine not getting enough air, or too much fuel, because of a faulty sensor. The hissing could be air escaping. I couldn't figure it out myself, so I brought the Corsa to a workshop. They used some smoke testing equipment to find the leak. With all those symptoms, it sounds like something more serious than just a minor issue. A faulty EGR valve could definitely be the culprit on a diesel.

Thanks for the info! I think you're right; it's probably best to take it to a workshop. It was indeed the EGR valve; apparently, it was completely jammed. The repair cost me 355€, but at least it's running smoothly again.