[ainarssems]

You should get VCDS lead even cheap e-bay one will do and check measuring blocks for MAF values, lambda voltages, fuel trim and misfires and knock sensor voltages before buying new parts. Some of these might point in right direction. In the meantime check vacuum hoses and engine breather hoses.

Are You coming to Christmas meet? Myself or somebody else can have a look at measuring blocks there if You do not buy cable yourself. That's assuming that car run reasonably well and do not misfire.

You can also swap lambda sensor from one side to another to see if fault follows and take out spark plugs to check if they look look running lean or rich.