I have checked the camshaft timing.

When it misfires, the exhaust goes oxygen rich but withouit any excessive HC.

It runs smooth with the throttle body connecters disconnected (As it does, breifly, if the fault code is cleared) so I would be surprised if it was a purly mechanical issue

(I did intitially consider the possibility of broken/weak valve spring(s) )

This is not a MAP sensing system