Many Intrusion Detection approaches for Vehicular ad hoc networks (VANETs) are proposed. However, not moving fake vehicles and vehicles with a plausible mobility model are not considered in other approaches. In this paper we propose an innovative signature based intrusion detection method that verifies vehicle movement data by applying a plausibility model. With our approach a single fake vehicle can be identified based on the plausibility model even if it simulates an autonomously valid movement. The results from the intrusion detection can be used to detect on the one hand road side attackers simulating faked traffic congestions and on the other hand attackers that try to deny real congestions by inserting moving vehicles into the network.