I've been working a while now on my 2003 X type. Previous owner sold it to me cheap because he couldn't solve this problem and now I see why. Typical cruise not available, bucking. Checked PVC hose and it's new, imt 0 rings had been changed but I changed again, the pipes to brake booster seem solid, no hissing. There is a slight bit of play at manifold where it snaps together but no hiss and I think that would have to be there. Next I'll either change the MAF or replace the upper and lower intake manifold gasgets. I'm getting the same codes I've seen other people who have this problem. Any idea on which is more likely? Car runs great in warm weather, check engine light often times goes out in warm weather on the highway but cold weather is another deal. It runs very rough, says cruise not available and bucks. I thought I fixed it with O rings because whoever put them on didn't clean the old ones off very well...I mention that because there may be something sloppy I can't see by a previous mechanic. I'm really at my whitts end on this one.