Think I have sorted it, found a melted wire about 8" down from the ecu plug it's an earth but there are two and only one had melted, looks like it melted some time ago and exposed the copper, don't know how it would cause this problem, but I have taped it up and inspected the rest of the wires and all seems fine. The car is now running and doesn't seem to have the problem any more, but only time will tell.