KonnyS

Hi everyone. 3 months ago I bought a 17 plate Audi A3 saloon with the 1.5TFSI and the S-Tronic gearbox and I absolutely love it but recently been having some issues with it and no one seems to know what's wrong. Whenever I start the car (regardless of whether the engine is hot or cold) it revs up to about 1200 which I know is normal but as it's going down it seems like it's going to stall then it revs up to 1400rpm and then goes down to 800rpm which as far as I am aware that's where it should idle (could be wrong) but then it's starts to vibrate and shake at which point the revs climb back up to 1000 and stay there which reduces the vibration and shaking. Had it looked at about 6 times in 3 months and I've had spark plugs, injectors, coils replaced as well as all the software updates done last Friday (17/9) and it still seems to have that problem. The engine seems to be quite loud when first starting it up, but previous cars that I've owned have done that and as they were warming up that would go away so that doesn't really worry me. Another thing which might not be something major. After I switch the car off there is a high pitched noise (kinda likw winding) coming from under the bonnet. I was thinking there might be a vacuum leak somewhere or one of the sensors not working properly so not sure as to what I should do. Any help would be highly appreciated. Thank you !