Why is my car oil pressure dropping when the car warms up? on 1998 Mitsubishi 3000GT

I recently bought another GT and I was wondering
My GT tends to drop in oil pressure when full heated up
It feels like it wants to shut off but doesn't..and when I'm driving it goes up but when I stop at a light it goes back down. And also it idles high when I turn on the heat
So I was wondering do I need to change a sensor or something
Any help or advice would do me some luck

As long as it doesn't go to low (0) then it is normal for any vehicle with an oil pressure gauge to be lower at warm idle than at speed!
Pressure can be checked with a test gauge to see actual oil pressure, at a repair shop.