Gas dryer not staying lit after start

Dryer Repair
1

When the dryer starts it fire up then goes out .I’ve check everything but the gas valve celanoids.But on top of the gas valve there is a white plastic adjusting screw about 3/8" with a lock nut on it that looks like its unscrewed to the top with the lock nut partway down the shaft in midair.Has this came loose and vibrated up.Or is the valve bad