have you changed/tested your ignition coils? or the "gas actuator slide" PN 000 141 79 25 if w/ASR and 000 141 78 25 w/o ASR ? this sits on the lower part of intake manifold, below air mass sensor? what about the air mass sensor?
I know there is a screen (PN 119 078 00 56) in the fuel distributer rail, I did not change it unfortunately. Mabe next time I take out the injectors.
The injectors are easy to get to and change depending on if your wiring harness is new and the vacume hoses are new or if you can get them off without breaking or crumpling in your hand. Putting it back together is more difficult since you have to line up all injectors at the same time so that the rail can fit on all of them at the same time. I think it would be better to mount the injectors on the rail first then placing the injection port end to the intake manifold all at the same time later.
I do not recommmend DIY since you have a lot of fuel and the chance of not reinstalling properly in the rail. If I knew what I was getting myself into I would not have done it myself.