Codes P0302, P0304, P0300, and P1399 (misfires) on a 2000 Honda Accord 4 cylinders?

I checked the spark plugs and cylinders 2 and 4 seems to be not tight enough. This may be the cause. But does a blown head gasket also causes these errors? I read somewhere that codes P030x on adjacent cylinders usually indicator a blown head gasket. In this case the two cylinders are not adjacent. I cleared the codes after tightening the two spark plugs and drove the car around the block and no error code so far. But this worries me a bit if the problem is more serious. Thanks.

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