is the helicoil a spring type or a real insert ? you might need a kit to chase the thread and put in a new insert. I had to put in a insert on the cylinder up front, go real slow, they strip easy and alot of our prepowers never used antisezie on the plug, and so comes the sriped threads if they did not, and oil on the plug does not do it, it is the other way it grabs the threads so it strips even more.

2001 5sp. K&N stock filter 215/70/15
If your check engine light is on at least you know the light still works