So for the 3 years I have owned this car, I have consistently had bad mileage, but as of recently the issue has got so bad that my car will stall out, and it still does not cause an engine light or code.

I noticed since around 11k, after fixing my turbo oil feed tube which was causing power loss due to lack of oil pressure that the car had a tendency to struggle to turn on on cold starts. I also noticed my oil level was never consistent, it was always periodically rising. It now to date gains 1/4L of fuel into my oil every 1000km. This is due to the fuel injectors getting stuck open due to carbon buildup causing all the fuel pressure to drop the fuel into the engine cylinders, which is why the car struggles to turn over in the morning and back fire constantly while its running.

The current fix is to replace your injectors and unfortunately its going to happen again as the carbon build up in these engines is extremely bad. At 22k I bore scoped my valves and they were atrociously bad, like a 250k car. At 22k I bore scoped my 2002 Jetta valves and they were clean at 288k.

There is nothing you can do about the carbon build up except add a catch can. It's just unfortunately these cars lack a decent pcv evap system and the car being direct inject in cylinder, its going to be a problem for the life time of the vehicle.