starts then stops wait a bit and starts

bit of help please ,rr 4.0 r reg ,started fine drove 40miles to pick up caravan.now on the way down the rev counter dropped and all dash lights flashed then went on as norm .sorted caravan ,rr wont start turns over but not firing left for 10 mins fires into life .runs pull fine 2miles latter shuts down ,wait 20 mins fires up again done this all the way back ,me thinking immobiliser and if it is how do I sort it .tried swearing at her .ps iv had a few p38s but never this problem

the symptoms are a classic for a failing crank sensor,ie runs then stops,cools down then runs again etc...

thank you I have cleaned the connecter and seems ok again now ,