do a tune up to eliminate all the minor things like plugs, wires, cap + rotor, fiel filter, air filter, plug wires. while duing this inspect all the parts to hel troublesoot problems if this does not help. but im leaning towards wires, maybe they are old or there is something preventing the spark to flow like water in the distributor cap or water in the plug chamber were the wires conectg to the plugs. know engines moove inside the engine bay specially if they are missfireing. so you can disregard that as a check, but checking your mounts would not be a bad idea. Good luck.