Look into your clutch fluid see if it is low, if its almost gone, you got a leak, most likely its either the clutch master cylinder, or Slave on the tranny, I would tell you from my line of work I reccomend, you replacing both at the same time, an then bleed it out, its a pain to do if your doing it by hand, BUT if your fluid is fine an not low at all, you wouldnt have air in it, ONLY time you get air in them, is if you broke the lines loose at one time, or have a leak, if the fluid is full, then you most likey have a clutch issue, need to take the tranny out to check it, thanks Joshua,