Q: Low fluctuating oil pressure when engine is cold and noisy lifters when driving over 50 miles an hour

There are several causes for low oil pressure. They include components such as crankshaft bearings, to things like an oil filter or pump. A leaking o-ring will cause some issues, mostly related to low oil levels.

The oil passages can become clogged and restrict flow. Oil lines can become clogged, and the sensor itself can go bad. Your exact make and model does have several accounts of the oil pressure regulator failing. You should start by checking this. If this is the case, you also need to make sure that this did not cause even more damage to the vehicle. Drop your oil pan and inspect for metal shavings of any shape or size. This is an indicator of much worse problems.

I recommend having a certified mechanic, such as one from YourMechanic, come to your home to determine if the oil pressure sensor needs to be replaced and if further damage has been done to the engine.