Ok so i have posted this in soo many forums, i thought that this should be good one to try. I have a 96 4.0 straight six with auto. When i got it when at a idle it would shake. It was noticeable on the steering wheel and in your ass. lol Though the tack does not jump, i have changed the iac,tps, plugs,wires,cap,rotor,fuel filter, clean throttle body, seamfoamed tank and throttle body, though no difference. There are no codes, drives fine after hit the gas, passed smog. So i put the scanner to it, it told me that the upper o2 was going crazy it was going from rich to lean to center back and forth. I was wondering if the o2 would make it shake