I wonder how the ELD works. Maybe it's a simple varistor? It sounds like when it's unplugged (open circuit) you get the highest idle, and plugged in with no load, the lowest idle. That would suggest to me that, if it is in fact a varistor, the higher the resistance (or the higher the voltage, I suppose) the higher the idle. A dead short on the sensor, or fooling it with a higher voltage, may lower your idle further.
Just a guess.
Edit: this might be helpful:
https://www.civicforums.com/forums/3...-detector.html