The dealer is a few miles away and said that they were happy for the scoot to be looked at by a local Yamaha-trained independent mechanic. This was last Friday when the scoot began to surge rather than idle at a red light etc.
Well, I set off last Sat on the way to the mechanic (whom I've known and got on well with for many years btw) - the bike was still needing to be turned off at the lights, yet at the final set of traffic lights the fuelling settled down to a normal idle speed. Would you believe it?! The engine light remained on though. Mr Mechanic plugged in his Yamaha diagnostic box only to find that it didn't bloody work either!
I've been commuting to work this week with the engine light permanently on but the bike running normally. I will be taking it back to the mechanic today - he has a new diagnostic 'box' - and hopefully, an explanation of the fault when he knows the fault code.
Fekin rigmarole but I will get to put the kettle on and have a gander at the bikes he has in!