I would disconnect the idle air control motor and see if the fluctuation stops. The ECM may be commanding the air control pindle in and out causing this issue. The ECM does this based on the input from the O2 sensor.
If the motor stops hunting, then you may have a bad ECM. That is what controls the motor.
I attached the procedure for the ECM below for you.
Images (Click to make bigger)
Wednesday, June 30th, 2021 AT 2:44 AM