Well...after months of issues since buying my 1.9 150 CDTI Signum I think I have finally got it sorted (touch wood).
Have had issues with a rough idle, poor mpg and a flat spot in accelerating over the 5 months that I've owned it. Can't say I've been very impressed with the reliability of the car so far... and that's coming from a former Alfa Romeo owner!!!!
Under warranty it's had injectors 2 and 3 replaced and new glow plug. I then decided to have DPF removed and mapped out which got rid of the flat spot below 2000rpm and made it much nicer to drive. Still had judder and idle issues though and VX said it was just a 'characteristic of the engine' and there was nother more they could do.
Took to independent VX specialist last week, had injectors 1 and 4 replaced, new wiring loom for injectors 3 and 4, and EGR mapped out. Now runs like a dream, pulls like a train and drives like I think it should.
It's been a long time getting there and would have cost over £1000 if it hadn't been for the warranty, but finally sorted. I spent £395 of my own money on an Evolution Chips remap with DPF and EGR removal and honestly think it was well worth it. I just need to run through a couple of tanks worth of diesel to see if the mpg is any better, as previously it's been pretty poor (39mpg combined when calculated at the pump, 46mpg on the computer! - that's more of a difference between the 2 than I'd expect!?!)
Hope this is of interest to others that have had these symptoms. I don't think the injectors were anything to do with it, but nice to have new ones anyway!