Surging Idle: Coolant Level and Thermostat
Thanks to both of you, Krusty and Salbertson.
Full Coolant: The coolant is full. I'd heard, since my original post, how important that was. It is full now, but the surging does continue. Thanks, though, for pointing this out.
Thermostat: This I wondered about. The engine starts normally, runs normally for a while--five minutes or so--then does its three to five minutes of surging before returning to the 750 normal idle. Would a bad thermostat act this way?
Thanks for your help with this.