Fiesta Tdci 2008 'Coughing' fault

Good evening,

First time here!

I have a 2008 Ford Fiesta Style Climate which has done approx. 78,000 miles. Not long after I brought it, it started 'chugging' whilst driving and idling and eventually the amber 'cog' light came on on the dashboard, the car went into limp mode and I had to get towed home.

It has since been to the garage where is flagged up injector 2 to be faulty. So a new injector later and a few weeks of driving it, the same thing happened again, flagging up injector 2 again. Back to the garage it went where is has been since May (yes, really). He's a good mechanic whom we trust so not worried about getting taken advantage of.

After speaking to him now, he has had the whole dashboard and computer, keys and everything sent off for testing and subsequently fixing. Now the car does seem better as long as you warm it up before going on a journey (which we tend to do anyway out of habit i.e. not taking off straight away and flooring it!) however there is still something not quite right with it and it still does 'chug' every now and then.

Our mechanic now seems to think that it is something wrong electrically as it went through the MOT absolutely fine and flew through emissions so indicates that the engine and everything is fine. However, looking for the electrical fault it like looking for a needle in a haystack.

Does anyone on here have any experience with this issue or have any ideas as to what it could be?! Some people have talked about similar problems but have not posted back with any solutions. Someone suggested the wiring loom but never posted back as to whether it worked or not or a Forscan reset.

Any help would be much appreciated!

ETC