Why does my car shake wen i step on the gas

Hello, There are several components that would cause this problem, and narrowing it down will take some diagnosis. If you have a check engine light, or other warning lights on, have an auto parts store scan it, and post the codes here. It sounds like you could be experiencing a fuel problem, ignition issue, or, depending on how it acts at different throttle positions, a bad throttle position sensor. It will take diagnostics to figure out. If you are planning on diagnosing on your own, ask me any questions you have, otherwise, here is a link to certified shops in your area: http://repairpal.com/cadillac-within-10-miles-of-houston-texas-77037

Most likely it is an ignition miss, but it will take diagnostics to determine the exact problem. Freedom Automotive can help and we have a 10% up to $50 discount going right now to help out.