crazy idle?

i have bought the 89 camaro rs  with 2.8 v6 it turns out it runs good plenty of power, but idles crazy.it will rev up real high, then try to die out,back and forth, back and forth, back and forth,can not get the key to turn backwards to check codes........im thinking some sensor maybe. maybe someone out there has hade the same problem? any suggestions would be nice...... thanks brian