2015 E350 Temp gauge

[AdyClarkeE350]

I have a E350 Diesel and recently the temp gauge has an intermittent fault ! on start up it can give normal readings and then the next time even when stone cold it reads 80-90 degrees straight away or flicks up and down like a tachometer ! When the fault is showing it soon rises into the red and then goes into limp mode and requests to stop.

Is it a faulty sender unit or loose wire, Any suggestions please?