No oil pressure when RPMs are below 2000

[cooperg]

Hello, I am new to this forum but am in dire need of help. I own a 1993 Jaguar XJ6 and when my RPMs are low (idle) my oil pressure gauge drops down to "0" and and the low oil pressure light on the dash lights up. However, when I rev the engine to above 20 grand, it goes right back up to where it should be "4". I checked the oil and there is definantly the right amount of oil in the car. The engine sounds pretty good but don't want to drive it with an oil problem and then cause a much worse problem. Thank you very much.

Any and all advice would be greatly appreciated.

CooperG