S3 chugging when idling / stop start function issue

Hi,

I've had a 2017 S3 Sportback for a couple of months (my first Audi - love it, never buying any other brand), and I'm noticing that for the first 5-10 mins of driving while the oil temperature is still heating up to around 100 degrees, when the car is idling at traffic lights, the revs are dropping to below 1000 and the rev needle is twitching, flicking up and down about 100 revs, and the car is kind of 'chugging' (best way to describe it). I can feel the whole car rocking while it does it.

It goes away once I've been running the car for more than 10 mins, but at times when idling it feels like the engine is going to cut out and is only just managing to run. I think it interferes with the stop/start function too, as I had an issue the other day where the stop start kicked in at some lights, after I'd been driving it for a few minutes, and it cut the whole engine and I had to completely restart the car.

Now I'm worried that's going to happen again so I'm switching the stop start system off every time I get in the car. I hate the feature anyway as it happens at annoying times like when slightly pausing to turn out of a junction.

The question is:

• Is that chugging normal behaviour after starting the car and idling?
• Should the stop start system not kick it while the oil temp is still heating up, and could that have been the cause of the total cut out, that it kicked in when it wasn't supposed to?

Any help appreciated!