From my experience stock coils degrade over time, and the more gap you run on the plug, the faster they die.

I went through 3 sets of coilpacks, each lasting a few months before I checked how my Iridium plugs were gapped and realised that they were too large/or gap had somehow opened up?

I changed to normal plugs and gapped them to appropriate levels for my setup and I haven't had a problem since.

 

those coils work because the 2.4 sonata engine back then is basically a Mitsubishi engine. they used alot of mitsubishi technology back then. the engine is a 4g6xx
the older sonatas had the 4g63 in them also. Good fine tho!