Peugeot 407 Wastegate Defect

Hello. I drive a Peugeot 407 as well and I encountered something similar a while back. The symptoms you describe, especially the loss of power and the hissing sound, are definitely indicative of a boost leak somewhere in the system. It could be a split hose on the intercooler, a faulty boost control solenoid, or, as you suspect, a problem with the wastegate. Have you checked the intercooler pipes for any visible damage or loose connections? That's where I found my issue before.

Thanks for your reply! I haven't specifically checked the intercooler pipes yet, but I will definitely take a look. When you had this issue, did the engine also stall at idle like mine does? And was your check engine light also on? If so, did you get any specific error codes? Trying to figure out if we are experiencing the exact same issue to narrow it down before I go to a mechanic...

Yes, the engine stalling at idle and the check engine light were definitely present in my case as well. Because of those symptoms, I took my 407 to a local reputable workshop. I advise you to do the same, because the issue is pretty serious, it is better to have your car checked by a professional mechanic. Boost leaks can cause all sorts of problems, and a proper diagnosis is essential to avoid further damage.

Thanks a lot! Your experience has been super helpful. It seems like I'm dealing with pretty much the same problem you had. I'll take it to my trusted mechanic soon. Finally got the car back from the workshop. Defect in the wastegate valve, just as suspected. Repair cost was 860€ Thanks again for your help!