do you have a vacuum guage?? if not, get one. it's fairly self explanitary. needle in the green is good. if it is bouncy, then there is a dead cylinder. WHY the cylinder is dead could be a few things, but one that comes to mind is a intake manifold gasket. a propane tank (like for camping lanterns) and a torch fitting with a rubber hose can be used (unlit) to 'sniff' along the intake where the 'miss' is. if the idle changes, you have found a leak. a can of carb cleaner could also do the trick, but can be tough to control in tight quarters.