Peugeot 408 diesel intake manifold leak

I have a Peugeot 408, and I experienced similar symptoms. Check engine light, reduced power, and rough running. Could be a vacuum leak in the intake manifold. Any sign of hissing?

I haven't explicitly detected a hissing sound, but it may have been masked by ambient noise. Could you elaborate on the specific areas of the intake manifold that proved problematic in your case, and whether any specific sensors exhibited aberrant readings, such as the manifold pressure sensor?

In my case, it was the intake manifold itself, likely warped from heat. I'd suggest taking it to a workshop to get it checked properly.

Following your suggestion, I took my vehicle to a reputable workshop, and their assessment aligned precisely with our discussion: the intake manifold was indeed defective, exhibiting scorching and subsequent leakage. The repair, inclusive of parts and labor, amounted to 1180€.