Sorry I'm not the expert, but I've subscribed to the thread instead of making a new one.
My car is Daihatsu Charade, its needle "DANCES" when I drive it under 30kmph, but becomes fairly stable after 40kmph!
The problem is not very big, it might be something wrong with the wire that connects engine to the meter . . .
Experts will help you solve the problem, good luck, drive safe