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Took my 2001 Focus SE (DOHC) to Advance Auto Parts today because I have idling / low power / stumbling with a check engine light. The clerk used the code scanner and found a P0301 and P0304 - i.e. misfires in cylinders 1 and 4. He recommended a new ignition coil, at $80.

Now I'm no auto mechanic but it seems to me that if there's a problem with the cylinders firing, the first thing to do would be to check the spark plugs. I don't remember the last time I had mine changed but it is definitely over 15,000 miles ago...

If you were troubleshooting this issue, where would you start?
 

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It most likely is the coil. Our cars, and most cars no-a-days, are a waste spark system. It fires 2 plugs at the same time, One coil for every 2 cylinders. 1 and 4 are companion cylinders and share the same coil and thats why they are both missing.
 

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does your car stumble when at high RPMs? When my coil went bad it would idle as it should and it would run as it should at low RPMs. The only time the problem was noticeable was at the higher RPMs.

if you get a new coil make sure it is for the focus and not the contour or zx2. The contour or zx2 one will work but they will require different plug wires
 

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x2 for the coil, I would also consider wires and check your plugs if you only have 15k on them. Pull them out give them a good visual and recheck the gap.
 
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