Peugeot 406 Intake Manifold Flap Issue

Sounds familiar. I have a 406 diesel as well. I had similar symptoms a while back: reduced power, rough running, hissing. Drove me nuts! Have you checked for any obvious leaks in the intake system? It could be something simple before you dive into the flap control itself. Imagine trying to blow up a balloon with a tiny hole in it. You'll get some air in, but it's a lot harder and you'll hear a hiss.

Thank you for your response. I have inspected the intake system for leaks, but my search proved fruitless. Could you elaborate on your experience? Did replacing the intake manifold flap control resolve the issue?

Yep, in my case, it was the intake manifold flap control, beyond any doubt. I tried cleaning it first, but it was toast. Honestly, save yourself the headache and just get it replaced. It's a fiddly job, and if you're not careful, you could make things worse. I'd suggest taking it to a trusted workshop. Better safe than sorry.

Thank you for your insights and counsel. I entrusted my Peugeot 406 to a local workshop. As suspected, the intake manifold flap control was defective. The replacement, costing 465€, has rectified the issues, restoring my vehicle.