As a key component of the future Vehicle-to-anything (V2X) communication technology, Vehicular Ad hoc Network (VANET) has a great potential of enabling real-time traffic safety and efficiency applications for people on roads. Therefore, attacking and misusing such network could cause destructive consequences. Wireless communication in VANET is based on IEEE 802.11p-based DSRC standard. Due to its inherited distributed contention resolution mechanism, the MAC protocol in IEEE 802.11p is more susceptible to jamming attacks. While preventing jamming attacks in VANET is not feasible, due to its unbounded scalability, detecting such attacks is primordial. First we develop optimization methodology for IEEE 802.11p MAC which defines its stability region under normal network conditions, this will allow us to determine detection threshold value to distinguish normal operation and attacks. Second, we implement the sequential detection of change method along with the developed methodology and we propose QoS-based Sequential Detection Algorithm (QoS-SDA). The important performance characteristics of QoS-SDA are accuracy and speed, while jamming attacks are detected with low probability of false alarms. Finally, we provide comprehensive analytical and simulation analyses to prove the validity of the develop methodology and the efficiency of the proposed algorithm.