I figured it out; I was using a stepper motor with a hugely different mix of voltage/current requirements. I'd recommend steering clear of using SparkFun stepper motors to drive your extruder =) Buying another, higher torque motor solved the problem for me.by nickp - RAMPS Electronics
Hi all, I'm having a problem with my RAMPS 1.3 electronics and the extruder motor. Whenever I tell it to move, it jitters one way for about half a second and then half a second later it begins to jitter the other way. I've tried plugging the Pololu board into another socket, and the behavior doesn't repeat even with the same board and motor. It occurs on either extruder socket (changed in firmwaby nickp - RAMPS Electronics