I read about using a vacuum gauge to troubleshoot and tune up, maybe it was on this site? It sounds interesting. I am using a dc motor with an optical disk, so no, it is not a stepper motor. I did have it setup like a stepper motor for the slow speeds before I implemented the PID code. Turn the motor, pause for 15uS after 3 holes, 64 holes on the optical disk. This allowed the motor to turn the speedometer at 1mph. Now that is done with the PID code. Otherwise, the motor would start at around 10mph.
