Change the sender unit as they are prone to failure and it is most likely that.
You don't need to spend £20 - £30 from Ducati, the sender from a Vauxhall Corsa is the same and can be had for less than a fiver;
http://www.ebay.co.uk/itm/Vauxhall-A...53.m1438.l2649
That said it could be an engine problem but definitely worth changing the sender first.