Has anyone come across a fault with PD Tdi engines in which the engine braking is reduced when the engine is fully warmed up? Not at all obvious when the engine is cold, completely obvious when fully warmed to this owner, but not a sudden step change as the engine is warming up.

This isn't gross enough a difference to convince a VAG specialist that the problem exists or is anything other than general wear on an old engine, but is big enough to interfere with driving pleasure.

I'm beginning to think it must have something to do with how fuel flow is regulated ... but have no idea really!

Put the trip computer into "instantaneous mpg" mode. When you lift right off, do you get "---.- mpg" reported?

A good thought, thanks. While I've been driving today I've been trying to pay attention and get some idea about whether the fall to ---.- is approximately even. Also been thinking through a range of other possibilities ... if anything specific comes to light I'll report back.