no they stay open, not all of them, think it depends which ones are open when the engine is switched off, they soon free them selves, one time I stalled the engine and when I tried to turn it over it sounded as though just the starter and ring gear was turning freely but not winding the motor over, then one cylinder started to get compression then another and so on till all 4 were ok again. it was tuning over very fast as though there were no spark plugs in the cylinders.