Tesco fuel doesnt help matters, in the past 2 weeks, ive cleared 3 cars with similar faults to your own, The exhaust emissions light was on... New fuel in and no more problems...
I heard of 2 more cars not the vag range having the same kind of faults, i'm putting it down to the fuel there using...
I'm no expert, but funny when all the cars are running on tescos fuel