Actually rust can sleep, just remove the source of oxygen...
To better answer your question I need more information, are we talking heavy surface rust but not much pitting, or is it suface but heavily pitted, or do you have areas were the rust has penetrated all the way through the metal. Depending on your particualr circumstance your treatment options will vary and it will also depend to a certain extent on what you want from the vehicle. To answer your general question there are much better products than muratic acid. Give me some more details and I'll describe some options.