AudiForums.com - PLEASE IDENTIFY MY PROBLEM

Can anybody help identify this problem.
My Audi a6 2.5 tdi had a slight tick in the engine when revved slightly or returning to tick over having being revved up.
I took it to a reputable non Audi garage, and the decision was made to put a new cam-belt kit on. The car is `R` registered and has 230 thousand mile on the clock.
While in bits it was discovered that the water pump was not good and so was replaced. The car sounded fine when it went to the garage.
When I got the car back:-
1, The car now sounds and runs really rough when cold.
2, The car sounds and runs better when warm.
3, The engine sometimes (when idling) speeds up slightly then slows, then speeds up again before slowing as if cycling.

The garage said the fuel injection pump may be faulty. I have had the pump checked (by a different garage and it is reported to be faulty) and luckily still working (but not knowing just when to inject).
Do the above symptoms sound like the pump is the true cause,of the really rough cold running. I would hate to have the pump replaced, only to find that the rough running is some other miss-demina that befell the car while in the garrage.
I am likely to be facing in the region of a £1000 bill just for the pump and fitting.
That is after the £550 just spent on cam belt and water pump (which took the car from having the slight tick, to something I could probably not sell)
In an amongst the rough running, I am sure I can still here the slight tick that started this job. The old belt was starting to tear an was caught in time, but was the job done right? and if it was, what a coincidence that the injection pump failed between going on, and coming off the ramp.

Any suggestions would be appreciated.

Best Wishes
Andy G