The fifth-generation mobile network (5G) provides extreme throughput and extremely low latency, which enables the Internet of Things (IoT) era and a series of smart IoT ecosystems. The widespread equipping of Device-to -Device (D2D) modules for vehiculars allows transmitting directly between devices without relying on central devices such as access points or base stations. This is the foundation for the shaping of mobile ad hoc communications, so-called MANETs. The combination of MANETs and IoT technology has led to the development of MANET-assisted IoT applications, which offer unprecedented capabilities. However, due to the mobility of network nodes, routing is one of the main challenges in these networks. To address this problem, we propose a multi-constraints routing schema to enhance the performance of MANET-assisted IoT systems. Our simulation experiments show that the proposed solution significantly outperforms traditional routing solutions in terms of performance such as latency, packet delivery ratio , and throughput.