I bought a 98 corolla awhile back. it runs good but i'm having real problems with the oil pressure, the engine had allot of gum build up in the pan so i removed the pan and cleaned it along the pick up tube. i also took the time to change the oil pump. When the car first starts it builds 90 psi of oil pressure (on and after market gauge i installed) after 10 mins of idling, until the car warms up the oil presume drops to nothing, the car does have 144k miles on it and im running 10w-40 in it. i was wondering if anyone has had or heard of the same problem. im thinking about rebuilding the lower end. Am i headed in the right direction?