A cap is positioned to contact a printhead when the printhead is not ejecting liquid ink onto print media. A dispenser dispenses an ink stabilizing material into the cap. A blocking structure is positioned in the cap to contact vent openings of the inkjet printhead when the inkjet printhead is in the cap and is in a location to submerge the nozzles in the ink stabilizing material in the cap. An ink control device draws the ink stabilizing material into nozzles of the inkjet printhead when the vent openings are blocked by the blocking structure. The ink control device subsequently draws the ink stabilizing material into the vent openings when the vent openings are separated from the blocking structure.