It happened to my Mazda/98, After i changed the engine mount, No more shaking.
I had bad shaking when idling in park or at a stop light. I replaced the timing belt and got the cams retimed. After that it was good.
put a good tune up on it if that dont work try addjusting ur ur timing it might be set to low
you most likely have warped brake rotors
might have misaligned or loose wheels
the cuase of this is ussaully worped rotars
Could be a problem with your torque converter
Cylinder miss, broken motor mount, or vacuum leak.
Engine miss or rough idle, or broken motor mount
rubber bushings in motor mount worn
Cylinder misfire. Possibly failed or failing engine mounts.
The engine of the car may need to be cleaned or your oil may need to be changed.
IAC could be the culprit http://www.ford-trucks.com/article/idx/0/170/article/Ford_Explorer_IAC_Fix.html
Normally this is caused by a tire out of balance or a bent wheel.