I had this a few years ago on my turbo, Pete.
Turned out to be one of the little black hoses (from the turbo or air inlet side, I think) had come off the inlet manifold. Just popped it back on and it was ok again.
Although, I've no idea why it came off in the first place
So check for loose or holed air hoses first (easy fix).
Cheers,
Karl.