Very mild hunting idle

[geezerman402]

That. At idle, the revs like to go up and down irregularly. Not enough to even register on the tach, but you can hear the engine going RRRRRrrrrrrrrrrrrrrRRRrrrrrrrRRRRRRRRRRRRRRRRRRRrrrRRRR. Totally inconsistent.

Can't find any leaks (though I haven't yet down a smoke test), cleaned the ICV, fuel and air filter are pristine... running out of ideas as to what it could be. Suggestions?

[DesktopDave]

Might still be the ICV.  They have a reputation for gradual failure.  Even cleaning them sometimes has little effect.

If you can pop the hood while the motor is hunting, just pull the connector off the ICV.  I've found that if this smooths out the idle the ICV is likely the culprit.  Of course that's really easy on M20s; it's a PITA on the M42.