I was thinking . If your paying £100 an hour for them to check the loom maybe just worth replacing it and then for the extra 50 its done or eliminated . Just a thought .
That would leave valves and ecu . I doubt itss ecu as its intermittent . And valves can be switched and checked whilts plugged into their diagnostic .
If they try to switch and check valves they still wont know if loom or valves and will need to check loom anyway . So i would think changing this would be an economical elimination .