Wah! If I can diagnose and fix a Valvetronic Double Vanos engine, I wouldn't be a keyboard warrior lio.... and I wouldn't have spent extra to get a warrantied unit from AB.. 
What's the mileage on the engine?
Standard troubleshootings...
Try spark plugs... not asking you to change but open them up and see how's the condition. You can tell a lot from the condition of the plugs. Our plugs can last 100k km.. they are NGK iridiums..
Air filter... see how dirty they are.. when was last change? if too dirty, it will starve the engine..
AFM... clean them with CRC AFM spray if dirty, or else leave them alone!
Check for loose wires connector or leaky vacuum hoses.
Other more serious culprits can be problematic ignition coils (we hv only 4, thank god!), loose ignition wires, clogged fuel pump, Vanos sensors, cam sensors, Valvetronic motors..
Best get SC to diagnose, pay them the diagnose fee if any just to seek their professional opinion. If they can't diagnose your problem, you are just wasting your $$ keep replacing parts trial and error done by outside workshop.
I wish I can help for a fee..
Maybe knocking or pinging... try RON97 to see if the jerk is still lurking around..
