Ok while driving my 1995 SC auto, my oil pressure stays around the M of NORM. BUt the past couple of days when I come to a stop and sit at an idle sometimes the gauge will drop and start to flicker and it will drop below the N of NORM, and sometimes it will even go real low and then my check guage light comes on. And twice the idle dropped lower than 500 rpm and stalled. I have no idea what might be causing this. Any ideas.