You don't short it. You ground it. It's a single conductor. Connect a wire from the connector to a ground.

The ecu controls idle speed with the ICS doodad only. THe only other idle control is a thermostatic fast idle valve in the throttle body which works off coolant heat. If the engine speed changes when the ign advance wire is shorted, the high idle is due to too much ignition advance at idle.

I think the problem is not the ecu. The most probable fault noted with a failed ecu is no spark, because the leaking caps eat the ign driver traces.t

Not responsible for advice not taken...