I have the same problem with my 99. Its a door pin that breaks off easily, and a lot of times without causing any noticeable problem until the door starts closing unevenly. This is what I was told when i took it to a Chrysler garage. Take it to a local body shop or dealer, they'll know what it is. The 2X4 trick only work temporarily, trust me I tried it multiple times.
Does the hinges look like they are attached to the jeep well? What happens a lot of times is that because the metal is so thin on the jeep that the hinge attaches to, it begins to break at the welds.
When you do the 2x4 trick, jack it up so the weight of the door is supported by the jack, then loosen the bolts on the door holding it onto the hinge, and then jack it up a little more. Then tighten everything back down again.
A forum community dedicated to Jeep Cherokee owners and enthusiasts. Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, and more for the SJ, XJ, KJ, KK, KL series and Grand Cherokee!