PID issues - with Code

[Ttelmah]

The integral term normally needs to be very small. It is what build the long
term correction for continuous errors. The derivative is what corrects for
the overshoot. Limiting the minimum respondable error, makes sense if
the motor control can't really handle movements at the detection limit.
This is classic if (for example) there is backlash between the motor and
the encoder, or if there is significant inertia in the motor.