Unusual coil misfire mystery
 

I've been stuck on a problem for quite some time now. I'm a 4th year and nobody in my shop could figure out this problem too.

99 grand vitara. 2.5L Started a year ago when I pressure washed the engine. I found the coils to be missing so I replaced plugs and coils. Still missing. Night time came and i could see the coils arcing. Cheap coils i thought. Picked up 6 at the wrecker and it ran like a dream. Few months later, all 6 are missing and arcing. I changed all the boots. Same problem.

Bought another brand of coils, still missing. Bought the highest quality brand I could find. $700 in coils and miss is still there. I'm mad. I drive the vitara hard. Like i stole it. Suddenly it stops missing. Weird. Drove it for a few weeks and the miss is coming back, but it would just be a miss here and there. Way better than before. What is my next step in diagnosis? I am really struggling with this one.

nobody?