Slow to start / longer than normal cold cranking time, idle roughness

[blubaru]

I have a new-to-me 2015 S4 with 30k miles. I noticed that on a cold start, it seems like the car is slow to fire up. I've never had a start failure but it seems like it is cranking too long. Subsequent warm starts seem to take a normal amount of time. I've also noticed that the engine idle can cause the car to shake a little bit, especially after the car is fully warmed up. It isn't super bad but definitely noticeable when parked or stopped, I can feel it through the seat. I had the car into the dealer for something unrelated and asked them to look into it, they said I had a very slight EVAP leak, which they fixed. I never had a CEL and honestly I didn't see any difference in the start up time or the idle after they fixed the EVAP.

Is this common with the 3.0T or is it worth taking back to the dealer?

[Iwantyourcar]

Common for me, but mine is a 2010 with 105k miles. I recently added a can of bg44k fuel system cleaner and it reduced the rough idle. Ive used this additive in many cars and had always had good results.

From reading around the rough idle seems to be common, as far as the slow start goes I don't know much about it.

[Rbb1485]

The 3.0t v6 cranking time tends to be a little longer than "normal" is the consensus around here...both ny 2012 and 2015 (current) displayed similar behavior, also the slight idle vibrating is also appears to be typical

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[Midnight_Rider]

Could be spark plugs. Start with the basics. Could be carbon build up. Could be bad gas.

My car vibrate, but only if left outside. When I'm parked inside the garage, heats up in minutes, no vibration. Could be it's just cold, and need time to warm up everything, like exhaust, and etc. Just saying.

[jygesq]

The vibration you feel the seat is not normal. A V-6 engine is not as smooth as 6 cylinder, in line engine such as in BMW 6. I do not observe any abnormal start time. The quality is gas you use can be a factor in start time an smoothness of engine. Only use Shell 93 . All my cars & my wife's car, seem to run better. Top tier gas is important to the way the car performance.Top tier gas also has higher detergents in the fuel?

[blubaru]

I may try some fuel cleaner and switching to shell 93 to see if it helps. The car only has 30k miles so hopefully the plugs aren’t fouled yet and there shouldn’t be excessive carbon.... at least I hope not.

[Iwantyourcar]

Bg44k. Good shit.