Resonance states of HCO are calculated for total angular momentum J=0, 1, and 3 using the artificial boundary inhomogeneity (ABI) method of Jang and Light [J. Chem. Phys. 102, 3262 (1995)]. Resonance energies and widths are determined by analyzing the Smith lifetime matrix. A resonance search algorithm and a method for resolving overlapping resonances are described. The accurate prediction of J=3 resonances from J=0 and 1 data is tested with good results for excited stretch resonances and less accurate results for bending resonances, demonstrating the degree of separability of vibration from overall rotation for these quasi-bound states.