Y axis won't hold when running a program

My machine is mounted almost vertically. When I start the machine everything homes well and I can use the joystick to move the spindle around anywhere I want. The machine holds position just fine. I was doing a ‘dry run’ (cutter about 1" above the material) of a program to surface my spoil board. The machine moves to the start position, spindle starts and it begins the first cut (at y=0). After the first cut it moves up in Y (Y=1.5) and then starts it’s return. At this point the Y axis just drops and falls down till it hits the ends of the y rails. The controller doesn’t notice and happily reports a Y position of 1.5". When it gets to X=0 it increases the Y by 1.5" and successfully completes that pass. At X=30.5" it advances the Y and when it starts to return the Y axis drops again. I did write the program by hand but I don’t see anything wrong with it. Here’s the start of the program…
G0 X0 Y0 Z0.5
G1 Z-0.02
G1 X30.5
G1 Y1.5
G1 X0
G1 Y3.0
G1 X30.5
G1 Y4.5

Any Ideas??

I should also mention that when homing the Y axis it seems to drop to the end instead of a controlled feed. It does successfully home and zero the Y axis.

You may need to up the idle current for that motor.

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