Hi, im pretty new here, and i looked through a bunch of the forums, but couldnt really find an answer. I hav a 98 Mustang GT, stock, and after starting it and when i "rev the motor" my RPM stays hi for a long time, then drops back down slowly. Upon start up it jumps to about 2000 or so...then comes down after mayb 5sec. One of the answers i found is maybe a vacuum leak? Does anyone know what it would be, and how much to get it fixed?? Thanks!!!