A couple of Quickie wire test..

When rainy, spray the wires w/WD-40 and then run the car...if that solves the skipping, change the wires.

Another test is just the opposite..spray the wires with a fine mist of H2O..if it skips , change the wires.

..and lastly, look under the hood on a real dark night w/engine at idle..looking for any plug wire arcing...you will see them in the dark.

.An oscilloscope tells all, but these are old DIYer tricks that work for those who have not the proper tools/equipment.