My magnum 2,7 does an anoying thing, when driving slow at about 1700rpm and not moving the accelerator the revs go up and down a couple off hundred rpms, you can feel the car go faster and slower, faster and slower and so on. What can be the problem ? No check engine light and no fault codes, any ideas ?

 

maybe you're driving right at the point where the torque converter locks in and out.