Oil Pressure Problems

Hi All.

Hopefully someone can share some light on this?

So ,when I drive my 1.8 Gti after 20 mins of driving the oil pressure light and buzzer sound until I blip the throttle and it stops.
Ive now just fitted a new sender unit to the side of the head which now makes my oil pressure gauge  work (which it never has)!
Wired it all in as per instructions and when I started the car the gauge was reading 2/3 bar or so, give or take.
I took it up the road and after a 5 to 10 minute drive the pressure on the gauge had dropped to just over 1 when driving and then when im off the throttle the buzzer sounds and light flashes. (as it did originally)
So I guess what im asking is :
A What should the pressure be at what RPM
and
B What might be making the pressure drop

The car doesnt use any oiland has recently had the bottom end barings replaced and the head skimmed.
Any help is much apreciated

Thanks
Dom

had a similar issue and oddly it was down to using the incorrect oil..i fitted a new oil pump " easy "diy job . and now run Halfords own make classic car oil.the 1.8 loves it car runs great with it and no more lights on ....could also be a mduff oil pressure sensor again an easy job and cheap part...ideally check your oil level if the engines 100k plus it wouldnt help to replace the pump any way ..failing this check the wires to the sensor and do an oil change ...i find these engines dont like modern light weight oils...after all its a 40 year old design of engine

All I have ever used was 10w40 in the winter, and 20w50 all other times, and where I live now I run 20w50 dino…..

From memory, oil pressure when at normal running temp should be 2bar at 2000rpm.