the rattle could be a million things - check this one i wrote two weeks ago -
http://www.automotiveforums.com/vbul...d.php?t=277222
the hesitation again could be a few things. did you swap the trans, motor, or both? what year/model was the donor?
in S-series the ECT tends to go bad on older cars, and the TB, IAC, and EGR can get quite drity, i alway start there, but they normally cause a high idle too.