Help 1999 mercury grand marquis spark plug
I was on the highway going about 80 when my check engine light flashed and went away I pulled off it was idling rough I shut it off and checked everything no leaks good fluids so I limped it the 70 miles back home with slight shuddering and a obvious misfire 5 miles away from the house my check engine light came on it was a cylinder 3 misfire this was the spark plug I pulled from cylinder 3 what would do this? Cylinder 5s spark plug was fine so I straightened the one in the picture ground electrode out and started the car for a couple seconds it sounded fine pulled the spark plug back out it wasn’t bent so I put a new spark plug and coil pack in it and just took it for a little test drive it seems to be ok I’m just concerned and confused I don’t even know where to start any help is greatly appreciated I love this car