For the longest time I have been chasing an idle problem. My 951 will idle at the correct speed, but extremely rough. I chased (and found, then fixed) vacuum leaks, found bad fuel injectors and a trashed AFM. I fixed everything and the idle only got worse with each step. I was really getting frustrated. Well, with the engine out of my car I found my big oil leak, my balance shaft cover was leaking. So I removed the pulley on the front to get the cover off, and I noticed something funny...... no woodruff key!! This makes it very difficult to remove the bolt by the way
So, even though I checked the alignment of my belts 3 or 4 times, the position of the pulley on my lower balance shaft meant absolutely nothing, and the balance shafts were still out of time.
I almost don't want to admit this, but I really have no idea how I lost it.
I have this hunch that when re-assembled, the engine will idle nicely and smoothly. What's really strange is that the vibration was only at idle, and not at any other point throughout the RPM range.

Lesson for everybody, when everything points to the balance shafts being out of time, don't stop when you see that the alignment marks are lined up, because the problem may lie deeper.

 

Hmmmm.....That doesn't sound right. The balance shafts will dampen vibrations at high rpm:s. For reducing vibrations at idle, the hydraulic engine mounts does the job.
Tommy

 

my car would shake at idle when up to speed it really didn't s hake that bad, my b/s belt was blown at the time bad motor mounts really make it shake