Under about 3500 rpms in all gears my car is chuggin really bad, kinda like when you have your a/c on and the car feels "sluggish" only like times 10 worse. The CEL light came on yesterday. Its at the mechanics and getting codes ran tomorrow. Any ideas?? I have a very loudly ticking fuel injector could that be it? It also puffin some black smoke,

help.
thanks,
Derek Johnson