Last week when waiting at some traffic lights my car starting to sound as though it was revving up, when I wasn't, the car was idle. As I was coming off the motorway this morning and slowing down to come off the motroway again it sounded as though it was revving up and then cut out comepltely. Wouldn't start again, was turning over but wouldn't start, until I was towed off the motoroway then has started fine. They could't find any error codes on the diagnostic maching, so any advice please???