Becca, I'm hoping you've solved this by now! But just in case, usually when a machine starts acting up out of the blue it has fuzz or thread in it, or maybe a burr on the needle. Try cleaning out the bobbin area, changing the needle and rethreading. Hopefully one of those will solve the problem!

Donna

Does it skip stitches on all zz widths, or only the widest ones? Generally, such behavior is indicative of a hook timing error.

thanks to those who offered suggestions. i followed up on them, but no joy. turns out that one of the plastic gears, very internal near the top of the machine, has lost some of its teeth. repairman didn't want to fix it because of time and cost, i think.
so. what is a good, inexpensive, second hand replacement?