oil pressure light is on

[tnm27]

Hey there guys, I have a some what simliar problem to like Bks5otrimGST, upset that mine is a 91 GSX. After the car warms up, if will drop below 1,000 rpm to about 600 rpm. When it does the oil pressure light turns on and it kind of studders like its going to die (similiar to a small vaccum leak). Also, my oil temp gauge fluctuates up and down, and will never stay at one spot. Has any one ever had this problem occur to them? if so, than how do you go about getting rid of this problem.