Have a unfixable problem
 

Hello I am a owner of an audi A6 2006(C6 F4 blb engine code) for the past 2 mouths I changed everything in the car(thats only in my mind only you can't change everything) :

​​​​​​- clutch kit fitted
- new egr valve
- new injectors
- new catalyst conv
- engine mount that was leaking
​​​​​​

So the problem is that when the car is cold only (first start of the day it struggle but only the first one), when I keep the rpm stady like 1.9k (on 3rd and 4th gear only) the car start shanking and the rpm are droping and riseing that makes the car shake, and does not show any codes. Reason that is in my head are:
- fuel pump maybe..
- they fkd fp the timing when they change the clutch by 1 tooth (chain)
- vacuum problem they said its okay cuz it does have vacuum

So before we end up changing the bolbs in the headlights to fix engine problem I am open for suggestions.

- Thanks for the help Audi fans

carbon build up, look that up

Is there a way to check ?