I need some help, so please respond.

Car: 1994 GSR

Miles: 178k

Problem: Once the car is warmed up, the idle should be around 800-900 or so, but it has the problem (which i think is the IACV?) where if you turn the wheel or turn the steering wheel, it jumps down to around 400-500 then back up. The big problem is once sitting there, the rev's drop down to sometimes as low as 100-200 (i don't know how it doesn't stall), then the oil pressure light comes on, the rev's go back up, and repeats usually the next time i stop (at a red light or stop sign). Does anyone know what this problem is? I know i need a new oil pan gasket and will get one, but I don't think thats the problem. I've been told everything from the IACV to a vacuum leak (which I don't know how to check). Thanks in advance for any help, and ill rep when i can (i almost instantly go on 24 hour ban )