We have presented an improved approach for the EZ-HZ formulation, by initializing the iterative process with (αo, βo) values obtained from the PM and the modal solution without losses, respectively. The efficiency and validity of this approach has been examined by analysing lossy dielectric-loaded metallic waveguides which possess analytical solution. The analysis of an image waveguide with lossy dielectric and conducting walls was performed. The results show that the number of iterations is drastically reduced, by nearly 40-50%, when compared withi the quasi-TEM approximation. Thus, excellent accuracy is normally achieved by using a small number of iterations even for the worse situations. Finally, we also point out the failure of the PM in the case of high losses.