Got a 2011 giant trance x4, was adjusting the rear shock today as the bike had been unused for about 6 months, it takes air ok and holds it as long as the pump is screwed in but as soon as you unscrew the pump it dumps all the air out the valve – is it a sticky valve and is it repairable – it’s a giant own brand shock. ta in advance

Check if the valve pin has come unscrewed. You can get a tool to tighten it up
valve tool

You could check if it’s loose with tweezers or pliers. If it is, i’d recommend using the valve tool to tighten up properly.

Sounds like the valve core is loose. It’s a schraeder valve so you can get a core remover/fitter