No boost and strange noise

[Jim Wallace]

I'm hoping someone can give me a few pointers. I have a 2012 E84 25D and recently I've been getting the following intermittent codes:

4862 Air System, Air to EGR Mass Flow, Plausibility

4873 Exhaust-Gas Recirculation Cooling, Plausibility

4530 Charing Pressure Control, Control Deviation

The car drove fine, no loss of power. I removed the EGR and Cooler to check them and there was very little carbon and both clear. Both were replaced around 10k miles ago under the BMW recall. 

The car has now gone into limp mode and is making a weird noise when reved. It's quite at idle but makes a lowish pitched drone or whining noise when the engine is reved. It's not a high pitched whine that I would associate with the bearings in the turbo. I had a fondle of the turbo spindle when I had the intake pipe removed. It spins freely and I cant feel any play in the bearings. The car has only done 55,000 miles and has a full service history with oil changes every 4,000 miles so I'm hoping the turbo hasn't failed already.  

I thought I'd try and check out the control system first. I looked at the parts diagram for the turbo vacuum control and started trying to check things. Connected a vacuum gauge on the supply side and the vacuum appears steady so I don't think there is a leak on the supply side or vacuum tank.  

I removed the vacuum line from the part labelled Vacuum box (15) on the parts diagram and the droning/whining noise stops. I connected a syringe to the Vacuum box and as i draw a vacuum the noise returns. Turned the engine off and used the syringe to draw a vacuum while feeling the actuator arm under the vacuum box and the arms moves/returns freely when a vacuum is applied/released. 

I can't work out what this vacuum box operates. The actuator arm passes down through the exhaust manifold and is connected to the turbo.

 

Can anyone tell me what this does or suggest any next steps to try and diagnose the problem? 

Thanks 

Jim