We have a toyota land cruiser diesel (IHZ) engine vehicle of 2003 model. It is completed 33500 kms. The problem is the oil pressure gauge needle remains at quarter mark in the idling and even in high rpm. I checked in the other vehicle and the gauge needle goes up in acceleration.
Replaced oil filter and oil pressure switch and gauge. Checked oil pump and strainer seems to be ok.
You need to put a pressure gauge on the engine and see the real oil pressure. If it is ok then you will need to replace a circuit board in the instrument cluster. I have replaced several and they are a little pricy. Good luck