The engine surges on my wife's car at approx 1700 rpm to 2200rpm. The car has 170k on it. It seems like it does it while trying to maintain speed and after you let off after acceleration. I drove it tonight and manually shifted it and it seemed to stay good after 2200rpm. When it surges it is usually 100rpm or so. The acceleration is good and the car start fine. There are no engine codes that come up either. I am kind of lost on what to check next.