That would require something analogous to muscle tissue in their "limbs." Sounds like more difficulty than it's worth, as fuel must also be distributed in some sort of circulatory system also.
But why would you do this in the first place? That kind of self sustaining would never work.
Nope... Even electrons are subject minuscule amounts of friction, when they scrape other electrons and such. It'd need some kind of power source, and really, the technology isn't there yet to allow precise control of free-floating electrons on such a small scale.
I'm not into Physics much, I only had a couple classes. All I can say for sure is that there would need to be some kind of power source, because self-sustaining motion is impossible outside of a vacuum.