Jerky stop and go motor is NOT good. It usually means that one of the 3 motor wires is not connected and that usually means that wire is burned out, inside the motor. Do not use "full throttle" to make it try harder because that may force it to burn out for some versions of firmware.
Have you ever seen any smoke at all? Or heard pop or hiss from it burning? Or found that it smelled like it was burned?
Use an Ohm meter to look for "open circuit" in the 3 motor wires. They should all look like they are shorted out to each other, direct connection from each wire to the others. Test all possible combinations of wires (call them A B C) so test A-B, A-C, and B-C.
So if you test motor wires (A B C) and find:
A-B is zero Ohms (direct connection / shorted)
A-C is open (meter does not change when you connect this)
B-C is open (...)
then you have discovered that wire C is "open circuit" and the motor is bad.
I have fixed one such motor, but I must say that for most motors, it is more useful to work you normal job for money and buy a new motor than to spend an hour or more fixing (rewinding) it. Just buying the correct magnet wire to rewind with will sometimes cost more than a new motor.