I’d suggest pulling the oil pan off and cleaning the oil pick up tube going to the oil pump. I had a problem with my '88 Escort a few months ago where the oil pressure was dropping to near 0 psi. I pulled the oil pan, took the pickup tube off the oil pump and cleaned it good by spraying brake cleaner thought it and washing all the sludge and dirt from it. The oil pressure on it is better than it’s been in years. This is an engine that has 517K miles on it and the oil pressure at idle is about 20-25 psi and at highway speed of 55 mph the oil pressure is about 55-60 psi.