Your engine has an automatic idle stabilization system, which should maintain a constant idle speed. When you shift from a drive gear to park the removal of the torque converter load will momentarily raise the idle speed until the valve closes down.
I think the OVP gets blamed for a lot of problems that it's not responsible for. Several have reported that removing and cleaning the idle speed control valve cured or mitigated idle problems. You should also carefully check the rubber air supply hoses into and out of the valve for cracks or breaks as several have reported them in poor condition. One other thing to check is the function of the throttle vavle switch and throttle linkage microswitch, and I found that partially disassembling, cleaning, and lubricating the throttle linkage solved a flaky idle problem I was having about a year ago on my 2.6.