That's a "new style" idler with an "old style" bolt.
The "old style" idler has one bearing inside, and the "new style" has 2 bearings stacked on each other, so really want a longer bolt. The newer cars come with a longer bolt. Go to your local Fastenal to get the appropriate bolt... I think 10.9. You can also get it from the dealer... let me dig up where I saw the part number... Gimme 5 minutes.
Edit: Here it is: http://forums.nasioc.com/forums/show...postcount=5780