The TPS will not be 0-5v, it will be more like ~0.25 to ~0.8v because most ECU's like a live zero and the TB won't rotate 90 degrees, it's more like 85 to 86.
Running this circuit directly from the vehicle's 12v system is suicidal. There is so much noise and transients it would be bad for any IC. Use an LM2937/40 as a hardened regulator to feed the circuit. Pick a voltage less than 12 and more than 5, 9 works well. These are cheap, rugged, and plentiful.
If you're only using 4 or 5 inputs on the 3914, you could make your own comparitor with adjustable trip points.
A small microprocessor would do this with minimal external parts and expense.
What does pot U1 do?