Help! smoking after repair

I have a 2000 Dodge Neon 2.0 L. While driving on the freeway a plug blew out when it did this the tube that goes through the valve coved also popped out and the plug bounced around in the valves. I removed the valve cover and didn't see any damage other that the spark plug hole in the head. The threads were gone most of the way down so I tapped the hole and vaccumed out the shavings. I put in an insert and a new plug. When I start the car it smokes and sounds like its not running on all cylinders. What should I look for or do to diagnose this problem. Any help would be very welcome. Thanks!