For the record: N1 below 40% below 1000ft is a criterion for an unstabilized approach in our outfit
Anyway, if the A/T is off, the servos are inhibited (even if the thing is is on and in ARM), there can be no motion of the thrust levers. However that does not mean that the idle N1 does not change:
The EEC will command approach idle when landing flaps are set, TAI is in use or when the EECs cannot receive signals about flaps or TAI below 1500ft. N1 and N2 will increase but the thrust levers will not move, and you have no way of going back to flight idle manually. Perhaps PMDG cheated a bit and simply bumped the thrust levers forward to simulate this? No clue.