Engine cuts out when down shifting

New to the forum and new to owning S3. Driving back from mot engine cuts out changing from 3rd to 2nd gear on 3 occasions. No undue noises and starts straight away after. Sorry if this is a basic question, but it's all a bit of a learning curve.

Diesel? Or petrol?
If diesel, my guess is the idle on the fuel pump is too low (had this problem after i passed my test, for 6months heel toe was the solution

Petrol. Garage played with the carb today, doing me a favour. Apparently. Is this likely to be the issue?

CrisC said:

Petrol. Garage played with the carb today, doing me a favour. Apparently. Is this likely to be the issue?

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if it is leaking air round spindle, it may have been set rich to stop this.

did they lean out mixture?

Is idle speed to low?

They've probably set the idle speed or mixture or both too low - if its a newer s3 the idle speed should be 800rpm (I do set mine a bit lower though). Much lower than that and the combined effect of lifting off quickly and slowing down causing the fuel to slop about in the float bowl can cause the engine to cut. Also, garages have a habit of setting the idle mixture too weak it should be slightly rich (to reduce NOx emissions at the expense of slight increase in CO - better for everyone's health when we're all stuck in a traffic jam!).

Setting up the carb yourself is probably worthwhile. A gas tester can help but doing it by "ear" usually gets you close enough - there are plenty of guides around on the net. A multimeter with RPM and dwell and a timing gun are good investments.

If you're not happy adjusting yourself, take it back to the garage. It would only take them a couple of minutes to sort. Good of them to adjust the carb so it passed mot but they've inadvertently messed up.