Well my friend this sounds like the same thing that just happened to motor, it was not getting compression in the number 2 cylinder. It started off as a mis fire changed the plugs worked fine for about a week. I notice the engine wasn't accelerating like it should. Very weak really hard to get up to speed. Drove it around for a bit then went to pump gas. Turned him back on and the idle got really bad almost like it was miss firing except that the engine was shaking really bad and the speedometer was reving all by itself. Had it towed to my cousins shop and long story short the number two piston lost compression. I'm unfortunately scrapping the idea of rebuilding anything. Don't have the time and these motors tend to give out even after being rebuilt. To each there own. Good luck on your build.
R.I.P 2001 Ford Focus SE 2.0L SPi