drive by wire - oh yes, you could utilise the existing TPS for position feedback, are there spare ouputs from the S8 to drive an extra actuator or multiple outputs for a stepper motor, or use a single output going into another stepper drive board which could convert the linear voltage form the output into the rotational pules for the motpor? only experience i've had with stepper motors trying to drive what can be a faitly heacy load (ie the throttle plate) you do need a big motor and power supply. when i was as high school, for my electronics gcse project i made "EIG" electronic index gears form my mountaing bike - worked ok, but u needed a trailer to carry the car battery to drive the motor to work the derailier

maybe a servo, then you could use just one output and use PWM to drive the servo, i know there are servos about that can respont quickly enough and drive sufficient torque from not that a heacy power supply.

would be an interesting one to play with nevertheless.