car shouldnt sound like a flat four, sounds like you still have other issues.
Is it still misfiring or just a very lumpy idle?
Id be checking for hoses that are not correctly fitted or leaking and that your exhaust is till connected fully and not blowing.
boost spike would be unusual if your DV is dead, usually its too little boost (but it can be a common failure)
things like PCV can also effect the idle running so worth checking too.
For a 2005 car Id also be wanting to pull the HighPressure fuel pump to check the cam follower.
Im afraid logging in VCDS is the only way to get the true picture, as you fix each issue as it comes up
First to achieve no fault codes, then actually logging on the road values for boost/fuel pressure etc
If you were sold the car like this, Id be tempted to start from the basics and do things like a compressions test just to make sure the basics of the engine are healthy.
Its just a matter of going through things step wise, using facts from VCDS and looking at things that are common 2.o TFSI failure points.
hope this helps
John
