OK i have a 91 rs 700r4 when i shift from park to drive it yanks hard like shake your head hard and people are like who man thats bad so whats up

 

if your idle is to high, or your foot is on the gas that will happen

your u joints could be shot, you can check the slope by holding the break and shifting from drive to reverse while some one watches the ujoint to see if it moves

The rear end could be shot too, not sure how to check that though.

 

I will sometimes get the same problem. I have a 91 Z28 and after the car sits for awhile I will back it out of the driveway and put it in drive, it will take a second to engage and them it hits drive real hard. It will shift hard going into 2nd too. It will only do it once and only if the car has been sitting for a couple days. I know that I have a sticky valve because sometimes when I am at cruising speed I can throw it in neutral, hit the gas and the car will want to pull slightly until the vave fees up. (Only a split second though, Not for long).

 

idle too high, with auto trans you want around 550-600 rpm,

 

My truck does the same thing. Its not the trans, cuz i got mine rebuilt and didnt do anything for it. It idles pretty high, around 700 when warm. Im pretty sure ive narrowed it down to the IAC.

 

Check your torque arm mount, it may be worn and your torque arm could be slappin around. Also, check your rear brake cylinders. If one is leaking, it will cause your wheels to move and jump forward. That's what mine was doing.

Ed