How do I size an isolation transformer I'm using to emulate a variable reluctance sensor?
It goes into saturation. When the flux rises above a saturation point, then the inductance of the transformer is equal to the air core inductance. So, except the series resistance nothing will stop the current rise as short circuit.

What you have to see is the volt second product. From the lowest frequency calculate half period, then multiply with voltage. Compare the volt second product with datasheet.

PS; Have you measured the output signal of the sensor? I don't believe it outputs +/-12V not nearly, you will burn the ECU!

EDIT:







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