Compared to conventional radar systems, passive coherent location (PCL) systems utilize transmitters already deployed within an environment. In this paper, we investigate PCL systems to estimate an unknown target position in three dimensional space, and propose a target-tracking process of three steps: 1) receiver selection, 2) target-tracking algorithm, and 3) filtering process. To reduce an estimation error of target position, especially Z coordinate of the target position, we also propose a receiver selection algorithm. The selected receivers can be utilized in the proposed target-tracking algorithm that successively estimates target positions in XY and YZ planes. Furthermore, in YZ plane, an estimation error of Z coordinate can be minimized by allocating different weights on each receiver's estimate. Lastly, a decoupled Kalman filter is applied to the target-tracking process. Simulation results show that the proposed target-tracking process achieves higher accuracy than other algorithms.