My '92 740 Turbo wagon has a speedometer that has begun to jump from zero to thirty while idling, and when driving it will drop to zero and jump up to thirty and back.
The wagon has another ailment at the same time, when accelerating and it feels the wagon should shift, it backs off, as if you got off the gas, or a governor clicked in.
Whether or not these two things are related or give a clue to the problems of each I don't know, but it they both are existing at the same time.
Any ideas?