Vw Sharan Odometer Problem

[Guest vwtel]

While sitting at the traffic lights, stationary, with engine running the odometer needle moved ip to 90mph, then to 120mph and then onward clockwise. Now when ignition is turned of the odometer needle rests in a six o clock position. When the ignition is turned on the odometer needle moves clockwise and bangs up against the stop at 0mph.

 

Any clues what I can do?