Youre thinking way too hard, a habit i have lol.
Unplug your Idle Air Control Valve and start the car.. It is on the throttle body, right above the Throttle Position Sensor. When your foot is not on the gas, the computer adjusts this to let more air in or not.
You can drive with it unplugged. The IAC itself probably isnt bad. What is happening is its probably getting stuck in its little hole due to carbon buildup. And with it have 216k on the clock, im assuming the entire Throttle body needs cleaned.
Let me know how it goes.
