First answer is "right on"- the threads for plug,- and if it is required, it is not easy, as the plug is way down in a hole, and not easily reached or visible! However, it is possible that somebody has used plugs with too short a reach (length of threaded part), and it is not engaging all the threads yet too! But even before that, I would check plug wires! They are not easy to get off plugs, and easily damaged. "Wires" are not really made out of wire anymore, they have a carbon conductor with thread wrapped around it, this easily broken if insulator pulled off plug improperly! Actually shoud take a special tool to lift them off plug, (but few have it available)!
Now about the sparkplug, - if it was right plug- and proplerly gapped it should not fail this quickly, unless you have some internal problem! My Neon is a 97, and I bouight it about 5 years ago, -- (around 60,000 miles ago), now it has 158 thousand on it! Still have not replaced the plugs! Had that missing probelm once, - surmised was bad wire, - but it cut in and out for about a month or two then cesed to hit at all, - I removed and cleaned plugs first to make sure it was not fouled plug. Bought used coil-pack at junkyard, put in, and it still missed part of time, took out and measured wires for resistance, - 3 of the 4 were damaged, (probably I messd up two of those taking out to check plugs)! Changed out wires, car runs fine, - that was 2'1/2 yeras ago!
I figure the burned out coil segment was my own fault -- for driving so long with bad wire, -- it burned coil out! But after fixing cars almost 60 years now, I have figured out that I do not "fix "anythng till it is "broke"! I do the obvious things like liquids, and oil changes filters etc, but have found that if you do not do those other "preventive maintainance" things till problems show up, parts last about 3X as long, and less things get broken while servicing parts that did not need any attention in first place! My old Air Force saying- " if it ain't broke don't fix it " applys here!
