cylinders misfiring?? fuel injectors?

[sileightysomeday]

yesterday i changed the fuel injector O-rings , and the valve cover gasket on my KAE. after i started it up , it now shakes violenty and sounds like a helicopter when i gas it. this happened before and i just drove it and then it suddenly just stopped. a friend told me it sounds like a cylinder misfiring. how do i tell ? and how do i fix this? if i keep driving with it, will it just fix itself like last time? when i rev it up it 's a little smoother but at idle it sits at 500 rpms, and shakes really bad. thanks for the help.