In recent years, Mobile Ad Hoc Networks (MANETs) have been focused on research and applied in many domains such as healthcare, traffics, military, entertainment, and smart cities. However, the performance of MANETs is rather quite. Due to the mobile characteristic of network nodes, the routing is the main issue to improve network performance. In this study, we propose a routing protocol, called IWCETT (Improve Weighted Cumulative Expected Transmission Time) protocol. This protocol is a modification of a well-known routing protocol, is Ad hoc On-demand Distance Vector, as a solution to improve the performance of MANETs. We adapted the mobile agent technology and a novel metric for routing in these networks. The metric is a function of the loss rate, the bandwidth and the end-to-end delay of the link. Indeed, we established a new tunable parameter to obtain a tradeoff between throughput and delay when computing the new metric. As a result, any routing protocol using this metric can always choose a high throughput and low delay path between a source and a destination. Hence, the achievable performance of the MANETs has been improved remarkably with our modified routing protocol.