Low oil pressure

What viscosity of oil are you using ? I would recommend that at 181K miles you use 15W40 at a minimum. At both idle and coasting you are allowing the engine to lower the RPM's which would lower the oil pressure anyways. As the engine has aged the tight tolerances have loosened up creating gaps that a thin (5W30) oil can not fill and you will see a lower pressure as well. You should be slowly increasing the viscosity levels from original manufacturer recommendations as you put more miles on the vehicle.

Sorry for not getting back sooner. I have been using 10W30, and I have checked the oil levels and they'er fine. There is a knocking once the gauge says zero and it idles for a minute.