Recommend replacing the spark plugs with Bosch F8DC4 plugs, gapped properly. I suspect the middle coil pack has failed, and the spark plug connector may need replacing also. If possible, swap a known good coil pack into the middle position and see if the engine runs smoother. From what I've seen online it's a better value to buy a complete ignition wire set (which includes 3 spark plug connectors) than buying the spark plug connectors separately.

White exhaust is usually due to coolant ... a bad head gasket.

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Fred Hoelzle