Just looked up info in ISV too ... I've not had to tackle that but looks like a good suspect for uneven tickover if you have eliminated vacuum leaks and checked the sensor resistance. The other thing that I'd check would be cylinder compressions. Broken valve springs are not uncommon and would definitely cause rough idling ... not so noticeable as the engine picks up revs. Good health check for a new (to you) car in any event.
Get your thermo switch changed out first ... at least that problem will have gone away
