92 Bonneville RPM and Oil Pressure Drop

[raiderlb]

I have a 92 Bonneville with 174,000 miles. When the car is in park with the engine running the RPM's are about 1100 and when the car is in Drive and the brake is on the RPM's drop to 600 or lower and wants to stall and the oil pressure drops to red line and the alarm constantly goes off, very annoying at a red light. The car runs fine under normal drivining except when you come to a stop. Not sure what to do any help would be greatly appreciated.

Thanks
raiderlb

[raiderlb]

p.s. Engine is straight 3.8 and this happens any time of the year in any conditions.
Thanks again
raiderlb