2009 3.0tdi lumpy idle.

[legacy4cam]

I am looking for some help tacking down the problem with my A8.

At idle the car appears to be on 4 or 5 cylinders, and when engaging drive or reverse causes a lurching effect which is most disconcerting.

It began only when cold, and I changed the glow-plugs initially, to no avail. Since then it has now developed to happen almost constantly when the car is idling. It has been on VCDS and had a coolant temp sensor changed (think it would have faulted when I disconnected to check glow-plug circuit was operating).

The car drives perfectly from 1000rpm upwards, is still economical, and has no visible smoke (DPF may be masking this). It does seem to "smell" very rich in the garage when started and idling, but that's not scientific, it never normally gets started and idle for any time inside .

Anyone any ideas, or suggestions of garages with diagnostic experience in central Scotland. It's been on VCDS , but I don't believe they will have spent time on injector measuring blocks etc, although if injectors were at fault, would they not generate fault codes?

I have searched online to look for similar issues, and ruled out glowplugs, coolant sensor, and the air distribution system is clean from looking at the throttle body unit upstream of the inlet manifold Y-piece.

Any suggestions or help welcomed.

Cheers,

Iain.