My Ford Focus has started stuttering. I put fresh diesel in a week ago, thinking that maybe it was the diesel that I had put in previous week, it normally does the stutter when I am in either 4 or 5th gear, when the car gets to a high rev,its though the car is starving of fuel. This is the second tank of diesel that I have put in and it is still doing this, I am worried that I will get stuck in traffic or it will stop on my way to work.

The car has 120,000 on it and I have had it for four years.