Toyota Repair: fluctuating oil pressure, oil pressure switch, oil pressure sending unit

Question
The oil pressure in my 96 Toyota T100 3.4L V6 has recently been fluctuating. When cold and when driving it appears to be normal but at idle it drops off drastically. How would I diagnose the problem?

Answer
The oil pressure gauges on the dash are not very accurate, the best way to verify the oil pressure is to attach a mechanical gauge where the oil pressure switch is located and get the true pressure reading. If the pressure is normal replace the oil pressure sending unit.