Audi Repair Questions? Ask a Mechanic for Answers ASAP
Is your level low when the light comes on? Because I don't think I ever see a light come on unless it is either empty, the oil pickup tube (and the oil pan) is sludged up, or the pressure switch is faulty
What viscosity of oil are you using? And what rpm does it idle at? The light is usually not active below 1400 rpm.
I would suggest removing the pressure switch at the filter housing and connecting an oil pressure gauge, see what it reads at cold idle, cold at 2000 rpm, and then let it warm up to operating temp and check it again. Either your oil is too thin (though you say it is fine for a few thousand miles) or maybe your injectors are leaking down overnight or overfueling while running, thinning the oil. Your idle seems a little high, it should be 800 or so. Do you have a check engine light on, or any faults stored?
Judging by your comments, I think the sensor is reading OK- so it is a pressure issue, which can cause problems if you drive.
I think since it happens after you drive 55 or above, then slow down, that you have some kind of sludging in the oil pan- the particles collect on driving for a while, and sit there until you shut it off. Then they drop off and scatter until the next time.