Incredible — super helpful! I’m brand new to this level of electronics, so this will be a learning project for me (and part of the fun).

Did a lot of reading and research and GPTing based on your guidance.
Here's my current plan of attack.

1.) Sticking with the stock actuator and VR speed sensor for now. I’d like to understand and work through the original system, even if it’s more involved. Baby steps.

2.) Use a DRV8833 or similar H-bridge to drive the actuator motor.

3.) Use an LM1815 or MAX9924 to condition the VR sensor and generate a clean digital speed signal.

4.) Start with a Teensy 4.0 or maybe a Pi Pico for the controller — probably using Arduino IDE?

5.) Goal is to get the actuator moving under control of the MCU and reading the pot correctly. Then read speed input and build out the outer PI loop to control speed.

6.) Great point re: runaway, had not even considered that: so, add fail-safes (brake switch, watchdog timer, limits) so I don't travel into the future.

I’m still a few weeks out from being back in LA where my car is, but I’m planning to order parts soon so they’re waiting when I get there. Again I have zero knowledge or experience in this department but it feels valuable to attain!

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1981 240D 4sp manual. Ivory White.