Help with basic voltage reducing circuit for auto

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am no expert here, but I'm guessing you could use an undervoltage sensing IC such as the MC34164P-3 https://pdf1.alldatasheet.com/datasheet-pdf/view/12086/ONSEMI/MC34164P-3.html
Have the normal power go through a transistor, when the voltage hits 3V, have current flow through the MC34164P-3 to the circuit as well as the base of the transistor to turn it off (perhaps a PNP with an inverter between it and the MC34164P). Between the MC34164P-3 and the circuit, have something that will make the voltage climb slower. Just my probably not so great idea, hope it helps stir up some better ideas.

Do you need to consider throttle position, rpm, and maybe time ?

I do not know, if you do not you need to find out.

It could be done using a couple of op-amps and a voltage reference IC but it's a bit long-winded.

Use a subtractor to get 0-1.3V divide it by 1.083 using a potential divider, then add 1.9 using an adder.

in this circuit, even though you're diverting away some of the current you're not changing the voltage at the point where the circuit splits.