[Engine] 1.6hdi Euro 4 Swirl flaps

[LucyLeBingo]

I've been reading a lot about 1.6hdi Swirl flap failure of late.

As far as I can tell they are located inside the inlet manifold.

What if any symptoms do failing swirl flaps give?

Is there a recommended interval to replace or clean the inlet manifold to prevent swirl flap failure?

Any input welcome, have you had it done or done the job yourself?
If so, at what mileage or for what reason did you undertake the work?

Many thanks all.

[IHateMyDadsM59Berlingo]

I wasn't even aware the DV6 had them even in 8 valve form or DV5.