I am assuming that the OVP refers to the Overvoltage relay. I did replace this relay (around $80 from the dealer) for another problem I was having. Obviously, I discoved that the vacuum to the EZL was disconnected after replacement of this relay. I now have a new overvoltage relay and my idle is high when the EZL is connected to the vacuum.
I suggest following the steps that the manual suggests. Start with the resistance mesurement of the idle valve, continue with the current measurment when engine is at normal operating temperature (current should be 700-1000 mA). If current is OK then you either have a bad valve or an air leak. If current is not OK then check the throttle valve switch, the wiring to the control unit and the other items the manual descibes.
Let me know your progress.