Erratic Ideal/Revs Gearbox or Engine?

[Flip-Flop]

My brother in law has a Lucida and he filled up from the same station, same fuel as my better half did on Sunday while visiting him and while speaking to him yesterday she mentioned the problem we have been having and it turns out he has had the exact same issue with his Lucida this week but he called the 'AA' and the man from the AA explained that this new greener diesel is designed for modern engines, on older engines the detergent in it can clean the injectors to the point where they stick, fingers crossed that's the issue although the fuel filter has been changed now (no vice needed).

*Just as a side note my BIL had to have his whole tank drained as his Lucida took a real dislike to it, ouch.