I've scratched my head, grumbled for a TSB, & fortunately been helped/advised by Forum Members here ... SO! I've found a VERY Informative PDF describing the OVP, it's functions, pin power status & applicability ... So here's some things to consider on this topic;
1. I spent $100 for the Idle Relay & installed it - No Change in behavior
2. MBDoc advised the culprit most likely is the OVP Relay
3. TAKE NOTE: If your ABS dash light illuminates when Hi Idle occurs, & goes dark when Hi Idle CEASES, the likely culprit is the OVP: it's interconnected to several systems & can react accordingly.
4. The Idle Relay costs somewhere north of my Social Security Check
5. The OVP = a case of beer (Guinness of course)

So! Have a Guinness, Replace the OVP, register & vote ...
54-242.pdf
Cheers

Uncle Tony