One of the hardest problems to diagnose is the traveling miss. It’s when a cylinder misfires and seems to move from one cylinder to another almost at will with no obvious reason. The primary and secondary ignition all check OK and the fuel delivery system shows no problems. You may think a vacuum leak is the problem and this is a possibility but rarely is it the problem.2 things can cause a traveling miss and the first is a defective ignition module which is easy to diagnose. Hook a lab scope to the power wire for the module and it should show the same number of spikes as the number of cylinders. If one is missing replace the module after checking the ground. The second is rare but we seem to be seeing it on a regular basis lately and that is AC voltage from the alternator. Here again it is easy to check and you don’t need a lab scope which is becoming rare when diagnosing problems lately. With a voltmeter hooked to the battery and set to the AC range of millivolts you should see no more than 0.4 or 400 millivolts. To further check and a easy quick check is to unplug the alternator and if the problem goes away then check for AC voltage at the battery to confirm your diagnosis.