A3 2.0T -- Rough idle at start-up when cold?
 

The title basically says it all. I've had a 2.0T cab for a few weeks, and have less than 500 miles on it. I've noticed in the mornings or the evenings when the car has been sitting for many hours, after I start it up there's a period of about 30 seconds where the engine shakes very slightly and the rpms bounce very slightly (less than 100 rpm variance; probably less than 50). It smooths out on its own if left to run for a bit, or after driving. This seems to be distinct from the sound of the oil pump doing its thing, which the owner's manual warns about.

It isn't a huge deal -- if it were a five or ten year old car doing it I wouldn't care in the least, and would just chalk it up to age -- but for a brand new computer controlled engine that runs flawlessly when at normal operating temperature it has my attention. Has anyone else experienced anything similar? Does it go away after the break-in period? Did anyone who has had the High Pressure Fuel Pump failure (the new recall issue) experience anything similar before the HPFP failed?

I've had my 2.0 cab since the end of Nov and can't say I've noticed this at any time. Just about to have my first 5k service next week. Hope it's nothing serious with yours.

I've noticed this only a handful of times on my 2015 S3. Each time exactly as you said it stopped in under 30 seconds. I have 800 miles so far and come to think of it I haven't noticed it in 100-200 miles I'd guess. I chocked it up to the engine being "tight" but I agree it's not something I ever expected would happen in a car of this level.

My S3 does this occasionally at startup. I feel like it didn't start til >1000mi (car has about 2500 now). First thing that came to my mind was fueling also.

My 2.0 does this as well at times

My S3 has done this 4 or 5 times as well. Its definitely not cold weather causing it either (I live in South Florida). So maybe fuel, but I only fill up at Shell's typically, so I'm not sure. I'm at 3700 miles and haven't had it happen for the last 700 miles or so. I'm still going to tell the dealer when I bring it in for the 5K.

So I've continued to pay attention to this issue. When the engine is all the way cold (based on the engine temp LED display, not outside temperature), the car idles at ~1,050 RPM. That's the period where I get the rough idle. After the engine warms up to at least two LEDs lit, the idle drops to 900 RPM. I've never experienced it after that point.

Separately, I've noticed that it's dramatically worse while I'm putting the top down if the idle is in that 1,050 range. I don't experience it while I'm putting the top down after the engine warms up. Given that the manual talks about the engine driving the oil pump (I think) at first while the engine is cold, I wonder if it's all somehow load related.