Why does the idle soar from 900 RPM to 1500 RPM in P when the OVP is removed? I have an occasional surge at idle that I am attempting to diagnose. My air valve and ICU have been swapped with another fully functioning vehicle and appear to be in working order. Perhaps my OVP is not functioning during these surges but why does it have the effect of controlling idle? Please pardon my ignorance and thank you in advance for any replies.

84 500 SEC