How can non-backed cryptocurrencies be stable (like by algorithm) Is it possible that a cryptocurrency can be stable, without being backed by another currency, for example stable by algorithm?

For example, when the value is too high, the algorithm will increased the number of new tokens created, or when the value is too low, the algorithm will decrease  the number of new tokens created. 

I would appreciate your help. Thanks.
It's entirely possible, but no one would invest in such a coin because the return on investment would be predictable and low, and the value itself would be subject to manipulation by the creator. You are basically describing how a Federal Reserve works, and a cryptocurrency that acted like a Fed is useless. 

Also, nothing in the blockchain indicates price, so you'd have to source price from an exchange. Each exchange price varies, so it's arbitrary and gameable which exchange is picked.