DS5 Turbo Lag Whistle

Sounds familiar. Had a similar issue with my old Volvo V70, although the engine was diesel. The symptoms seem related to the turbo system. Could be a boost leak, or perhaps a faulty boost pressure sensor. Have you checked for codes?

Codes? I haven't hooked it up to a reader yet. I'm guessing the whistling is probably pressure escaping somewhere, but could it really be the sensor?

That whistle is concerning, definitely points to a leak. But a faulty sensor can cause all sorts of weirdness with boost control. Honestly, with those symptoms on a Citroen DS5, I'd take it to a workshop to avoid further complications. Better safe than sorry with these turbo systems.

Cheers, I appreciate the advice. It was the electrical bypass valve, like you said probably something with the boost control. Cost me 250€ to replace. Runs like new now.