2001 Elantra oddness.

So here's my situation. My '01 elantra is running rough again. It stumbles at idle and at any rpm below about 2500.
This started last December. I had the code read, and it showed a
cylinder 3 misfire. Because it was going on 120k miles anyway I replaced the spark plugs and wires as a guess, which solved the problem completely at the time.
Now the problem has come back. Because it worked last time (and because it cost around $10) I replaced the spark plugs again. Yes, I know that it's not normal to have to do so this often, I just wanted to see if it would solve it again, and to see if something was fouling/damaging the spark plugs. No such luck, it's say 40% better, but still bad. So I found an autozone, had the code read, and this time it shows a cylinder 1 misfire and a "major evap leak". The kid then asked me if I had done any damage to my gas cap lately. No, I didn't think to get the actual codes, but I could get the codes read again if that would help anyone.
So my question for all of you is what part of the whole fuel vapor capturing system (which I'm only mildly familiar with) would cause this, and where should I look next? I'm assuming that even if the gas cap weren't airtight that it wouldn't cause engine problems like this.
Any thoughts?
Thanks Ben
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Richard Dreyfuss wrote:

What did you use for plug wires and plugs? There are a lot of really junky aftermarket wires out there. I've had good luck with NGKs, but they can be hard to find in stores. As for plugs, the stock ones are Champions, but NGKs also work well. Another possibility is a problem with one or both of the coil packs. Check that they're solidly mounted and that the wire connections are clean and tight.
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On the first change (which solved the problem) I used NGK plugs and autozone brand wires. More recently when I changed the plugs, I went for cheaper ones, autolite I think. The thought was that I could get cheap clean ones now, and see if some other problem was damaging the plugs. I can get better ones though.
I should have mentioned, with the more recent problems I pulled off and checked the coil packs. The resistance of both on the secondary coil was just barely at the bottom edge of what's acceptable in the shop manual, which made me curious, but since they "passed" I put them back. They had almost identical readings, so there's no clear winner of which to replace (since on the two different occassions that this has happened it's been cylinders 3 then 1, which are on different coils).
I suppose I could do coils/good wires/good plugs in a last shotgun effort to solve this, but if you have any additional suggestions I'd love to hear them.
Thanks Ben
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My money is on the AutoZone wires.
You don't need to have the codes reread. They were P0301 and P0455, and neither has anything to do with the other.
Since we already know the misfire is on cylinder #1, here's what I'd recommend. Remove the engine cover and pull the #1 plug wire off the plug. Then set it back in place on the plug without clipping on. Start the car. Then gradually lift the wire off the plug and observe the spark in the hole (or anywhere else it's occurring). The spark should be coming out the end of the wire and jumping to the plug or the plug tube. If it comes out of the side of the wire, the wire is bad. If it comes out of the coil, the coil is bad. If it comes out between the wire and coil, the seal there is bad, requiring at least new wires.
I've said this before, and I know many people disagree with me, but I find factory wires to be an excellent investment and will consider nothing else for my own or customer's vehicles.
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Richard Dreyfuss wrote:

I would bet that's your problem, though it still could be the coils. The only wires I know of that are pretty much guaranteed to work well are NGK, Kingsborne, Magnecor (expensive!) and the factory wires. The factory wires are somewhat pricey, but you can probably get them faster than the less expensive NGK or Kingsborne, which typically have to be mail-ordered. Magnecor wires may well be the best on the market, but they're expensive. I'm running NGK plugs (V-power) and wires and they work great.
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<snip>
Sure enough it seems to be. I bought a set of wires at the dealer, and for the moment at least the problem's gone and the car is running smoothly.
Thanks to you and Hyundaitech.
And boo to autozone branded parts.
Ben
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