I've never seen one of these before. I wonder if it works. :rofl:
http://cgi.ebay.com/ebaymotors/Scion-xA-xB-tC-Matrix-Jetta-BMW-O2-Simulator-CEL-FIX_W0QQitemZ250128389085QQihZ015QQcategoryZ33629QQrdZ1QQcmdZViewItem

here is my homemade one
http://i11.photobucket.com/albums/a156/gammatnt/car%20stuff2/o2sensor.jpg
got it from Advance Auto Parts under $5

Works great with my DC header.

The tC guys use them to stop CEL with aftermarket headers.

However, this isn't an issue with headers for the box... but yes, they do work, and are often times necessary.

Search for antifouler in the tC area... you''ll find lots.