My 86 305 shakes alot at idle and when I am going a steady speed the car kind of feels like something is pushing it back and forth. I thought it was a transmission problem because when it starts to shake and I hit the gas ever so slightly the tranny downshifts( the tranny is a overdrive auto.), and the shaking kind of stops but when I let of the gas the tranny up shifts to overdrive and it starts alll over. A man at the Autozone said the problem is a Limp cylinder, and to fix it I have to replace the spark plugs and spark plug wires. But after doing that the elky still does it but not as noticable. Has anyone ever heard of this or was the clerk just trying to make a sale? I have no idea how to fix it. is there something else that I can replace or check?