Audi A6 Competition 2016 - Cold Start Issues

[riflo]

Hello guys, hope you are enjoying the life a bit 😄... First time posting here

I have an Audi A6 Competition 2016 3.0 BITDI (326hp). I have more than a year tracing an issue.

I’ve been having a strange issue with my car during colder weather (around 4°C to 18°C) and was wondering if anyone else has experienced something similar.

On a cold start, the engine fires up just fine. The idle RPM is slightly higher than normal(see the image attached higher_cold_rpm.jpg and normal_cold_idle.jpg). However, if I press and hold the throttle to bring the RPM up to around 1200–1400, the engine starts shaking and the RPM fluctuates up and down.(see the video issue.mov) If I try to do the same thing, it is gone  and everything is normal except the high idle RPM which is 900 RPM and after 2-3 minutes it drop to 820-850 and after 5-8 minutes it drop to 800. Also a unpleasant smell comes out from a car's exhaust(maybe wrong air/fuel mixture)

On warmer weather I don’t have this issue at all. The idle is still slightly high(the same as on colder weather) on cold start, but there's no shaking or RPM fluctuations when I press the throttle.

From the past, the normal engine RPM after a cold start should be a bit higher than 800 RPM(maybe 820-850). Now the idle RPM is 900 RPM and after 3-4 minutes it drop to 820-850 and after 5-8 minutes it drop to 800.

So far I’ve checked:

• No error codes stored (I scanned with a diagnostic tool – nothing came up)
• Injectors tested and all are within the spec
• Throttle body cleaned (minor carbon buildup, nothing major – cleaned the whole area shown in the image engine.png except the EGR Valve)

What do you think I need to do next of if anyone else has experienced something similar what did you fixed?

Thank you guys
Flori