Bought used car big mistake but I gotta fix it (rough idle)

First eliminate all vacuum or air leaks in the system and make sure the EGR valve is closing all the way and doesn't have carbon stuck in the pintle. Try cleaning the throttle body. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle.