Mystery Pop

[Halon]

There is an idle switch (on/off). It's on your throttle body, usually a single green wire going to it.

When you let off the gas, that idle switch signal is sent to the ecu. It's either on (1-indicating idle) or off (0 - indicating not idle). If that switch went bad, or the wire broke, or it became misadjusted for whatever reason, then that signal may be stuck at a constant Off / 0 / not idle. So if you have a logger, can you see the idle switch on/off signal? If so, see if that signal changes between on/off when you press the gas pedal, and let go of the gas pedal? If it never changes, than that may be a reason your idle suddenly changed overnight.