Hi, Re posting the same old problem after few months.
Car: Audi A6 99 2.8L Quattro. 113Kmiles

History: Started having low oil pressure problem since Apr 2011
1) Checked oil pressure and they all checked out fine as per my mechanic
2) Changed oil pressure sensor or sender and still same issue
3) No noise when light comes on and car runs with same power, no other abnormalities
4) Have been driving like this almost 6months without any issues but annoying beep without any damage so its not real pressure issue.

After so much observation below is the pattern, after a bit of driving and when car reaches normal working temp around 150F to 200F, low oil pressure warning starts only at 1800RPM.
Took car on plain empty road and did a test.
1) Drive below 1800RPM - No light
2) Drive above 2000RPM - No light
3) Drive app around 1800RPM for morethan 2Secs - BEEP BEEP and light comes on, if I press acc or remove acce light vanishes.(more over its city driving where car runs at 1800RPM)

I know that oil pump runs faster if engine revs fast and slow when env revs slow.....
Million Dollar question -- Is it oil pump? or something else like engine rev sensor or anything gurus here can think off??

I am very determined to fix the issue without throwing money at it guessing as this is my winter car and love to keep it for short drives.

Thanks for reading.

*************** 11/19/2011
Issue resolved after changing Oil Pressure Sender with Audi OEM part, $20 from dealer

Per Audi specs at 1800RPM pressure has to be between 17-23 psi and pressure sender opens
the one which was isntalled was not OEM but from NAPA which doesn't open untill 25PSI where it should close between 17-25, the one from Audi closes when pressure is 20PSI, thus sending wrong signal to instrument cluster.

My mechanic (Audi enthu) was doing this test by supplying air pressure valve to the switch and figured it out and saved me without changing any costly parts ;-)

Kudos to him

 

I will say what you know all along:

It can be the sensor or the pump. I will replace the cheapest part first and see if that resolved the problem. A dealer will replace both.

 

any more ideas are welcome..
if not oil pump is on my list as I already tried oil pressure switch.

Any clue what parts I would need?
automd says I would need, oil pump (for sure), oil pan gasket and oil pump gasket.

But couldn't locate oil pump gasket online.. is there one for this 2.8L 30V engine?