Idle is not referring to N1, but fuel flow. The throttle may be at idle as indicated by bolding.
The minimum fuel flow is adjusted to approximately 750 lbs/hour. An altitude may be reached at which this minimum fuel flow equals that required for maximum exhaust gas temperature. In this case retarding the throttle to idle will not change the power condition. The flight may be continued at constant altitude. In the event that the maximum EGT is exceeded, it can be reduced by losing I altitude and increasing airspeed as outlined in SECTION II, "Altitude Control".