1999 Mitsubishi Eclipse Spyder Gs 2.4l

I need help. I got this car off someone else. The timing belt broke and he had the head fixed (I am guessing the valves) And after all he said ran very poorly. I got it and the starter went out so I had that replaced. Had a camshaft position sensor code, so I replaced that. Still has the code even after resetting it. Well Check compression and has good compression on all cylinders. Firing order is right , getting sparks to all the cylinders , the fuel injectors is working. New spark plugs put in but fouled out I am guessing so I put old ones back in to fire the motor. Balance shaft belt broke and replaced that as well as the crankshaft position sensor. Now down to the point. Car will run but poorly, Idle up and down , Was told there was a misfire in #3 n #4 cylinder. But it is getting all the components it need to fire. Was thinking when he put the head back on he forgot to hook up something important or something for it to do this. The camshaft position sensor code is up and bought two sensor and they both still show the code but the engine will run. At times it will not show code but at times it will. Had gas in the oil , but it could be from excessive starting , but what else could gas be going into oil? Any help would be appriciated and I will reply back with more information as needed thanks