Must be the most unreliable engine I have ever come across. My 1.6TDCI is playing games ... again... it feels unresponsive and very hesitant to accelerate! The engine has done 94K miles, I service it regularly, every 5K using Total full synthetic oil. The car has had the DPF removed and a remap to get out a bit more power. Also recently I changed the Mass Airflow sensor. Not sure if it has anything to do but recently fixed the alternator (new regulator and rectifier). I can hear a slight whine and a knock which sounds like coming from the top of the engine. The turbo feels to be working normally, it boosts normally at least. There is a slight flatter sometimes when I take my foot of the accelerator but I think that's because I removed the dpf.
I came up with the following possibilities which should help/fix the problem:
1. new injector seals/o-rings.
2. using BG244 fuel treatment.
3. using BG109 engine flush on my next service (next month).