While investigating the reason for a slightly high tickover, I realised I don't really understand how the Metro air inlet works. There's a hose from the manifold going to that plastic widget with 'AC' on it, then to a vacuum cylinder connected to the flap.Doesn't the temperature control it in some way? The hose on the manifold had perished so it probably hasn't worked properly for ages. Disappointingly that isn't the cause of the fast tickover.