im guessing that pushing 100kw / 200~nm out of that tiny turbo, relentlessly, on a baking hot day, might have been a factor in it - no turbo likes that sort of thing. another thing that springs to mind is the exhaust - depending on the design (i know it's not full turbo back), it might be facilitating the kind of boost creep that may send the car into limp mode, because exhaust gasses are escaping too quickly for the turbo post-tune?
or then it could have something to do with exhaust temp sensors post-tune on a hot day etc etc...
i'd be looking for someone with vag com, or at least drop by your local dealer's and ask them to download the fault codes (shouldnt take them too long).
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