Arduplane either intermittently starts the motor or doesn't start it at all. Even in manual mode

After arming the plane. The motor will not follow the throttle commands. It will either randomly start the motor (even with throttle to 0) or it will not start at all when the throttle is increased. This is the same for whether the plane is in fbwa mode or manual.

Sometime when the plane is disarmed the plane will spin the motor. I’m at my wits end now. Any advice is appreciated!

Sounds to me like the motor is wired to the wrong channel.

Post a parameter file and hopefully somebody can look at it and give some more specific advice.