As Metalman said; it's the vent tube for the automatic transmission. As for the misfire, you should have it looked into by a shop with a dealer level tool. It could be as simple as needing a coil replaced, but I wouldn't start throwing parts at it until you find the true culprit.
Try moving the #3 coil pack to cylinder #1 and see if it follows, if so then you have evidence enough to buy a new coil.
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