2003 Focus TDCi rough running

[Devil2575]

About 6 months ago my Mk1 Focus TDCi started to run rough. It was noticable when pulling up at a giveway line, lights etc after driving at a decent speed for some time and was felt as a vibration in the cabin. A quick rev of the engine and it went back to normal. After a while this started to get worse and even after reving it was still not as smooth as it should be.

I took it to a garage who couldn't find anything wrong with it. They changed the fuel filter, put some forte engine flush in the tank and after a week or so it went back to normal.

The other day it started again. Normal running is not as smooth as it should be but it is frequently a lot worse when pulling up after driving.

I'm tempted to stick an engine flush through again as it seemed to work last time but I can't help thinking there must be an underlying issue.

Any thoughts?