I have a Volvo S40 (diesel) and sometimes I have a problem around ~2,000 RPM: it is something like a limp (or you could say that the car hiccups)
Strangely, when my brother drives the car, he does not have this problem, it only happens when I drive.
Also, could you tell me at what RPM should I drive? I usually drive at around 2,000 (but, I am used to a gas engine, I've only recently started driving a diesel).
It has manual transmission
EDIT: last time when this happened, I went to over 3x1000 t/m and it solved the problem for a time.