Check out my link of a few days ago with photos and replies.
http://www.peachparts.com/shopforum/showthread.php?t=295086

I was wondering the same. What I did was put a bb in each of the two vac lines passenger side bound coming from the 5-way connector above the Vacuum pump. On my SDL there is also a heavier black line (plastic, and filter) grouped with the mentioned vac lines which apparently threads to the cabin for fresh air to the valve. That line I just left alone. I had suspected vacum leaks in either the ARV, ERG, or connectors.

I may be off base...who knows but at least you can see the photos and member's ideas. Runs very well now.