To enhance the QoS performance in saturated multihop adhoc networks, it is essential to have cooperative algorithms for MAC layer contention resolution and TCP layer congestion control. This paper proposes a cross layer approach that modifies the back off mechanism and congestion control technique using Fibonacci sequence. Due to the golden section property of Fibonacci sequence, contention and congestion can be effectively controlled. The NS2 simulation results show that the proposed algorithm drastically enhances the QoS performance of 802.11 multihop adhoc networks.