Scud,
When you say "oxygen settings" do you mean the CO trim (carbon monoxide)? If so, then, by all means (guzzidiag/Axone/VDSTS) check your CO trim - these are notoriously lean from the factory.
While there is no special TPS, it is common that its potentiometer develops a little glitch at the most common throttle openings. I only found my fault by connecting it (TPS) to an Ohm meter and very gradually opening and closing it which revealed an abrupt *jump* in resistance. I could not see it watching millivolts.
Give your throttle body plates a good clean as well as the idle air bypass screws and their receptacles.