Just a thought..
I had same issue. My indy shop wanted to replace wire set (which had just been done a year previous) and forums suggested everything from bad coil to coolant leak.
I pulled plug, looked fine. Replaced it, and set the plug wire with a slight tap with a socket extension and hammer. The code hasn't been back in over two years.
I'm sure I got lucky, but again, just something to consider before you spend any $$.
Good luck.