A3 2.0 TDI Juddering HELP PLEASE

Hello i wonder if anybody come give me some advice please.
I have a 2.0 TDI A3 2004 156000 and it has started to judder like mad and some times cuts out.
When the accelerator pedal is pushed down hard i coughs and splutters but if you lift of for a split second it goes off.
I have removed and cleaned the EGR and anti judder valves and have this morning replaced the diesel filter and it is still doing it but since i have changed the filter i have noticed the tick over is erratic..
I am stuck and hopefully somebody will have an idea to what it could be so any ideas please.
Nick

Thanks for the reply been to an Audi/VW garage this morning and he said tandem pump oil seal most likley cause so taking it in Friday morning...

Finally know what the fault is thankgod..Inners of fuel tank flaking away and gone into the fuel pump..
Took pump out of the tank and it was swimming with flaking fragments..
So now i know what i need new tank and pump..