Poor tick over and lack of power.

[Fester]

Hi folks,
I have a 2003 Audi A4 2.5tdi cabriolet. At the moment its idle is rough and irratic and it is very down in power when driving. You can put your foot to the floor and it just doesn't go.
I have changed the MAF sensor as garage said it was faulty after looking on fault code reader.
This problem appears to come and go, drives ok for weeks then this occurs.
Had a good look around engine and can't see anything obvious that would cause the issue.
Any ideas folks.
Thanks in advance Tony

 

[Fester]

Just been out in car and fault has disappeared. Tick over normal and pulling like a steam train throughout the gears. Very mind boggling indeed.