Engine Misfire-HELP!

About a month I was driving right down the street from my home, when all of a sudden I heard a noise & the engine quieted down. My car would not accelerate past 20mph. Went to a repair shop where they did a computer diagnostics. Was told that I had the wrong type of spark plugs & that cylinder 1 had a burnt spark plug coil. Also the Ignition coil pack needed to be replaced & engine treatment due to carbon build-up in the intake manifold. I personally replaced all those parts myself & the engine still shakes with no acceleration beyond 20mph. Put a can of Seafoam into the gas tank as it was recommended by many people I consulted with.
I drive a 1998 Chevy Cavalier 2.2L w. 204,000 miles. Thank You Very Much