Uneven motion in X and Y directions after attempting to adjust Z motion in ADVI3++ A few weeks back I updated my Monoprice Maker Select Plus from the stock firmware to ADVi3++ 3.0.2. I've put more than 20 prints through the machine since then and everything has been fine.

One of the few downsides to the new firmware is the Z control. When moving the head up using the control panel, it only moves a millimeter or two instead of the 5 or 10 is used to, meaning it can be a bit of a pain to clear the head out of the way when working with the printer. 

I wanted to adjust the setting, so I went through the settings section of my new firmware, trying different values for various options to see if one would change what happens when I pushed the up arrow button for the z axis. I was careful to only ever change values for the Z axis, and after each change I set things back to where they were. 

I never did find what I was looking for, but that will be a topic for a future question.

The very next print after doing this came out awful. I can no longer get a clean, straight line. Instead, the edges are all wavy... and it's way worse than simple ringing. On longer linear stretches I can observe the print head does not move smoothly, but rather speeds up and slows down. It never really stops, but it doesn't move consistently, either. It kind of pulses as it goes.

I have duplicated this with a known good gcode file, so I know it's not the slice. I can move the bed freely with the printer off, and this started on both axises simultaneously, conveniently after my z-axis experiment, so I don't believe it's a problem with bearings. 

I've tried restoring factory defaults and even re-flashing the firmware, but it hasn't helped.

Any ideas on how to correct this?
Found the problem. 

The screws connecting the carriage plate to the assembly that connects to the Y-axis belt had loosened, allowing some free play for movements in the Y direction and vibration for movements in the X direction. It just happened to go from nothing to unprintable all at once at the same time I was experimenting with the Z settings.