No change with the starter fluid test, but the issue had started increasing in frequency, and I noticed the rear-wing started deploying when I first started the car. Time to replace the battery (best I can tell, Origianl battery from 2005). Car idles like a champ now, so I'm guessing it was some interior mechanism forcing a high-idle to keep the voltage / amperage up where it should be, or just a weird electrical gremlin side-effect of the dying battery.