Bit of an update but not with any real outcome.
Still not had any time to fit the TCV (never buy a project house
) but I did notice today after a cold start I get a screeching noise when on boost. I could only reproduce this 1-2 times before it went away and could no longer repeat it, so it only happens when the engine is cold I guess.
The engine ticks a little on cold start too so wondering if it's an exhaust manifold leak. Would explain the screech on boost and ticking on cold starts but doesn't explain the lack of boost when hot as usually the leak would close up.
It's booked in on the 29th so will see what the garage says.