635D low end sluggishness

[kwaka jack]

My 2008 635D has recently become sluggish at the bottom half of the rev range. Once the bigger turbo kicks in about 2800rpm its no problem. I've been doing some googling and while I can't find anything specifically on the 635 a fair few sites are coming up with turbo actuator valves are a common fault for sluggish 3 series.

Has anyone got any ideas of what it could possibly be? Are actuator valves common to fail?

[MajorBeef]

I had this on my 535d. Turned out to be a boost hose. Was £200 or so for my mech to locate and replace it.

[helix402]

As above+check all vacuum hoses for splits.