I just bought a 97 avenger with 112k on the odometer. When I am cruising the whole car will "jerk" as my wife says. It's kind of a shimmy as though it were misfiring, however if the vehicle is under load or coasting it runs fine. I have the auto wit hoverdrive and if it starts to shimmy and I turn off the over drive it smooths out . At idle it has a consistant misfire, if I try to push it above 4,ooo rpm it acts like it has a rev limiter, (the tach sits there bouncing off the 4k line) I had the local Autozoner check the computer codes and it just gave me something I didn't under stand. Actually I had it done twice, the first guy said it was probably just a dirty airfilter, so I changed it. The second guy said it was my gas cap either being too loose or too tight. Thanks for your help.