Just doing an underbonnet check and spotted something I'd not noticed before. It's a threaded brass? stud in the left (when standing in front of the car) side of the airbox, which hopefully you can see in the pics. No sign of anything missing or having been attached and I assume the airbox is common to this engine in other applications where the stud may have a purpose. 

There are loads of ecoboost pics on here but couldn't find one showing this - they mostly show coolant pipes for obvious reasons😀.

 

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I was wondering this the other day, I took a guess and thought it was a sensor that was used in the Mk7 version of the airbox as I remember one being tucked into a little nook around there

Ah, could well be. Trying to get a better look this morning but pic below is best I could do, very tight down there. Does look more like it could be used for something like a sensor rather than a plain stud though.

Anyway, at least I feel more reassured that nothing has dropped off! Thanks @sioneon.