How often should you have to replace the coils on a 5.4 in a 2001 XLT? I bought one about 2 months ago wih 114K on it and had to replace 1 when I got it and my mechanic had to replace on at his expense about a week ago (he got it wet during a radiator flush) now today I went out and started it and got a check engine light and it was running rough after sitting overnight and I suspect its another coil. I will get it on a computer tomorrow to find out for sure but I wanted to know how often do these need to be replaced or do you just do it as they fail? How could one fail just sitting in the driveway overnight? Any help would be appreciated.--Thanks!

