My car, now instead of just the hanging rpms, jumps about 200rpms everytime I take her out of gear. The rpms jump, hang, and then slowly drop. I know mustangs are notorious for the hanging rpms and i've experienced it from day one, but now they jump! WHAT IS THAT? Does anyone else experience this? Is the egr valve or something else going bad and need to be replaced? Oh yeah, I noticed my mpg went down the toilet also since she had this problem. Can anyone help me? Thank You!