speedo going hay wire when driving help

[alotmentman]

hi ti all ive got a xreg renault clio ..1,2 petrol car ....the speedo is reading that im doing 140 mph////wen only doing 30 mph ////ive replaced the speedo sensor with a new one which solved the problem for a few mile now im back at square one ,,its floating all over tha place can someone tell me wot the fault is and how to solve it thanks

[colin324]

Could be a wiring fault elsewhere, or there's water in the connection. Knowing the French, probably a connection issue as they like putting lots of connectors in weird places.

[steelcityuk]

This is a long shot but it could be just electrical interference. If I put my iPhone in a holder clipped to the central air vent of my XM the tacho goes wild.