The PW2000 and F117 engines are controlled to EPR at power, not N1 (assuming normal operation - there are failure modes where control reverts to N1).
N2 speed control is used at/near idle, as is minimum burner pressure (PS3) (i.e. at idle, the control will control to N2 or PS3, doing a 'select high').
Turning on bleed doesn't change the control loop response, but if the N2 rotor is flirting with separation or stall (not an uncommon problem with this engine type, mainly the earlier builds), the rotor speed changes can simply be more rapid than the control can respond to - there are significant lags in the time between the control senses N2, the fuel flow changes, and the resultant torque change results in an N2 speed change. We're talking fractions of a second here, but that's all it takes to set up an oscillatory rotor speed response. When controlling to EPR, the time lags get worse, because of the inherent lags in sensing EPR compared to rotor speed, making an oscillatory response even more likely.