I have a bad coil pack, should i replace the faulty unit or is this a sign that I should replace all three coil packs?

 

I had a faulty one about 6 months ago and just ended up replacing all three packs and plug wires at the same time. I did it myself and it ended up being about a 30 minute job. I'd do them all at once because if one is going bad, the others might follow shortly.