I have a 98 Merc Mystique, I took my car to a local dealer and had them do a diagnostic on it, they informed me that the car needed a major tune-up. I have changed the plugs and the timing belt was replaced by the dealer a month ago. My problem is surging, everytime I am accelerating, the car acts as if it can't make up it's mind on what gear it wants to be in and it surges. There are certain speed ranges though that do not cause this problem, it only seems to happen when it's going through the gears or when its caught in the middle of a gear change. Can anyone help me on this?