rough idle

I have a 1997 malibu v6 3.1,it has a really rough idle.When the air condition is on it doesnt really idle rough at all.I have taken to 5 places and they all tell me different things.I am stuck I dont know what to do.It is very fustrating that the mechanics cant fix it.It sucks because the engine light is not on and the mechanics say they need it to be on to find the problem.I thought that they were supposed to be mechanics!!!!Anyways if anybody could help me at all,I would really appreciate it.

hey there i have a 1998 chevy malibu with the 4cyl and i have a really rough idle and i dont have a ses or check engine light on either i did and it was the catylitic converter and i replaced that and did not fix it. the mechanics can not find it and it is really getting on my nervs need it fixed if you can help please reply
shane

lately when i turn my 97 malibu (is a v6) on it idles at around 1,500 rpms and stays like that until i shift into something else other than park. otherwise it idles at 600 rpms, like if i drive and stop and put it in park or whatever. i can't firgure out why it is doing this