Nissan Repair: Nissan 300ZX Oil Pressure Fluctation, oil pressure switch, nissan 300zx

Question
The oil in the engine is 10W30 the ambient temp is approx 86 degrees.  When the engine is cold, the oil pressure is about 60 PSI, after is warms up it drops to about 30-40 PSI when cruising at about 2500RPM.  Then oil pressure at idle drops to near zero with a warm engine.  No valve tapping the engine idles very smooth, runs great.

Answer
Troy,

Either you have a defective oil pressure switch or the pump/main and rod bearings are worn and this is causing the pressure to drop off.  Change the oil pressure sensor first and if you have the same result you are looking at pulling the oil pan and inspecting the bearings and possibly replacing them along with the oil pump.