Could be a lot of things. I don’t think it’s the pump or the relief valve. I don’t think the spring could possibly break. It could be stuck slightly open. Could be the filter and the anti drain back valve.
If it has shaft rockers, the rocker shaft ends could pop a plug out or knocked itself sideways.
you could have water or fuel in the oil diluting the oil
if the car is slower and there is a misfire or even just a lower idle speed, the oil pressure will be lower. 20 psi is a lot tho.
