97 Bonneville stall,low idle,irrattic idle

[sdp]

I have a 97 Bonneville,this is my problem. The car will idle down too low when in drive and the brake applied,if I am coasting into a turn at like into a drive way it will either stall or act like it is going to,if it dose not it wii idle up real high.Then when in park it will idle up high acouple of times and the even out. I have no service code. I changed pvc valve and without the o ring on it runs fine if I put the o ring on it acts up. Can anyone help? Thanks