You can use one of those little hand held propane torches to check for vacuum leaks.
DO NOT LIGHT THE PROPANE TORCH AFIRE
Just open the valve on the propane torch, allowing the gas to hiss out....move the tip of the torch around the manifold and vacuum hoses....If rpm'* change, you've found your leak.
A spark plug with a really tight gap could cause a random misfire associated with that particular plug.
Also, how are the brakes....could be a ruptured brake booster causing the vacuum leak. You could pull the vacuum hose off the brake booster and cover the hose with your hand and see if the miss goes away (obviously, have the engine running ).
Last edited by 1.8TTony; 09-29-2015 at 01:16 AM.