[juld0zer]

Firstly - unless your pockets are deep, stop firing the parts cannon and invest in some diagnosis.

The idle issue with the AC on or coming to a halt is a well known issue and I am going to assume yours is a DCT as I've not heard of it affecting manual cars. edit: Missed the bit about putting it into park. The software update addresses this issue. There are several threads on the forum about this including one very detailed one which details one owner's battle.

What was the service history like? It sounds like the previous owner was never fussed about it or the car rarely saw a dealership. Has it had all the recalls done? (junction box cable, driver airbag, VANOS?).

Is there any tune or piggyback installed?
20L/100km is ridiculous. Mine averaged around 11.5. Still crap for a 3L motor.

You should also reset the adaptations after installing a new MAF sensor.