No the 3100RPM is NOT the "fast idle" setting, bit it IS from the early 308s Owner's Manual!! "Warm the car at 3000 to 4100RPM until the Temp Gauge begins to swing" or something like that! I can only guess it was to actually build oil pressure, and build heat faster in the all aluminum block... Once you releasa a partial throttle opening at the gas pedal a slightly warmed engine will idle at 800 to 1,100RPM in my experience.. HTH
