Engine light came on, first time ever (148k miles). Engine running rough. Suspected bad cylinder. Auto zone free code read says misfire on cylinder 3, 5, 6. I pulled couls and plugs in 5 and 6. Plugs looked rusty and coils had small cracks on back.

 

I just did this last week on my car. (245K miles)

Replaced 1 coil and all the spark plugs and that cured that problem, but then had to also replace 1 cat in the middle as well. (I replaced them both)

Also make sure the MAF is securely connected and the spark plug wires are fully plugged in after your job.

 

the gap on your old plug looks way off - the center electrode looks ok, but the ground electrode is burnt away

 

i checked the gap. .039 I think... and it was spot on. planning to replace one coil (#6) and all the spark plugs.