2003 Audi TT shuts off on left turns

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I have a 2003 Audi TT 1.8T, with around 130k+ miles. The engine completely turns off ONLY when I make left turns or U-turns. Sometimes the whole car will shut off causing my steering wheel to lock up in the middle of the road, forcing me to put it in park and come to a complete stop before I can fire it back up. When I do successfully complete a left turn, acceleration stutters very badly. My car has been in the shop for a week now and apparently they can’t figure it out. They said 20+ error messages came up in their computer, they diagnosed them and I guess everything seemed fine. They asked me if the owner told me anything about the car being tuned before I got it, I was never told that by the owner, but the mechanic said the possibility of not keeping up with the tune might’ve messed up the computer or something?Lastly they suggested I go to a dealership, but maybe they should’ve suggested that before I spent over 1k on them trying to ‘figure it out’ (they replaced the acc. belt and tensioner, and replaced the ac compressor because it supposedly locked up and caused the belt to snap?) therefore I pretty much refuse to leave there with my car still broken. So I have to wait 2 more days for their master mechanic to come. I just get the feeling i’m waiting around for him to tell me the same thing. For the record my knowledge of car maintenance is scarce. If anyone could please help somehow, I would greatly appreciate it.

Yes, sometimes it takes a dealer. I’m surprised with all the error messages they found, your check engine light was not on.

Almost everything you need to know about maintenance is in your manual .

Apologies, I should have mentioned CEL was on before diagnosis. They cleared each error as they inspected them, no problems so they say. Test drove the car for about 15 mins with CEL gone, engine dies on a U turn, then again on the left turn back into the shop, CEL remained off, that was 2 days ago and they say the light has yet to return after they test drove it. I should also mention I’ve always had issues with the CEL staying on after repairs.