CPS sensor - mine had this prob a while back - water ingress to the CPS caused it! it is at the front of the engine at the bottom (fly wheel side). un plug lead, undo single bolt then leave on radator overnight! Then try again, if this fixes it, replace it or dry again and seal the end with a smear of epoxy resin! - that got me home whern I was away for 2 days then I got a new one!