Adding Brake Caliper Cable Tension SRAM Rival
It sounds like there is an issue with the return spring rather than the cable tension.  If the brake is pulling easily and not returning, I'd guess it may have become disconnected during your removal process.  I would compare the setup of your return spring on your working brake with the one on the non working brake.  It maybe as simple as clipping the spring wire back under a tab of some sort.  It looks like on that model brake the return spring is a coil wire deal on the back of the brake.