http://www.**********.com/Images/products/large/1168000473_VDO_40937279.jpg

i believe this is the cause of my vacuum leak. ive checked all the lines for my door locks and my trunk. the all hold pressure but this thing does not.but how do i tell?
I think its in my door because, when i block off the hose that connects to this
http://www.**********.com/Images/products/large/1268000078_FEB_D18BD03A.jpg
my engine shuts off fine..(doors dont lock ofcourse but it shuts off)
Am I close to my problem?

its an expensive part and if its not broken i dont want to buy another part i don't need.