I am amazed at the number of posts with the same problem I have with my oil pressure. Even after replacing the oil pressure switch, changed oil and replaced the filter, the reading goes from "0" to 40, back down to zero. Makes a difference whether it is in gear (manual), in neutral or just idling. Other than replacing the oil pump, what else could it be? Could the gauge itself just be bad. No one that I find has ever posted the final remedy.