Hi Im Scott

These were notorious for engine misfires which were often spark related. You are on the right track believing it to be spark plugs. What often occurs is carbon tracking forms on the spark plug porcelain resistors (it usually is visible and looks like someone has drawn lines along the porcelain with a lead pencil. it is actually the same thing) the carbon tracking allows what is essentially a short to earth and when under load the spark looks for the easiest route which is along the tracking, not over the electrode which causes the plug to fire, as a result you end up with a missfire. It is mostly much easier to replace the plugs and spark plug leads together. you can also opt to help stop this from occurring again by adding some "heat sink grease" this is applied all over the white porcelain and insulates it. It was regular practice at the Hyundai dealer I used to work at.