I think the way most folks test this is to unplug it and plug the two plugs
together.  If your idle is steady then the stabilizer is probably bad.  If it
is unsteady I have found that this is usually always a vacuum leak (keep
looking you will find it).
I have these stabilizers new for $50 (1.9l only).

Thanks,
Ken Wilford
John 3:16
www.vanagain.com
Phone: (856)-765-1583
Fax: (856)-327-2242

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