Why my car vibrates badly?

check motor mounts and transmission mount.locate mounts and get someone you trust to help you.raise hood,start car and have someone sit in car,put in drive while holding brake pedal,you will be standing beside car with feet and body away from car looking at motor from side while driver holds brake in drive and pushes gas pedal a little.see which way motor leans and how much,then put in reverse and give a little gas and watch motor,it will move a little but you can tell if it is to much.if motor has a lot of movement replace mount,whichever one moves, tilts the engine the most.also sometimes you can look at the mount and tell if the rubber is broken inside it.one other thing to check,i should have put this first.check fo vaccum hose leaks under hood,if you have a vaccum leak,it will make your engine run like crap when under a load.vaccum leaks cause alot of problems,listen for hissing sound,run you hand on and around hoses to see if engine changes or smooths out,start with that first.good luck.report back with what you find wrong.