High Idle when engine is warmed up while in park

I have a 89 ford probe gt, when i turn my engine over and it warms up it idles between 1500-2000 rpms if i drive it for a little bit it ends up dropping back down 750 , but itll still rev up to 1500-2000 rpms randomly and them stop and go back down to 750. I dont know if its the IAC valve or if its my throttle position sensor. I have checked some of my vacuum lines and from what i see there arent any leaks. Should i adjust my valves ? Or what? Im in the process of replace the valve cover gasket and oil pan gasket and timing belt cover gasket as well as the crankshaft seal . Will any of these things help my idle lower ?