had that on my 1st wrx. the spring is a complete B*****d to get to (Hands to big) but it should be the source of your problem. i'm betting its missing/snapped.
look at the second picture here on the right. this is the spring you should have and shows where it goes in relation to the rest of the linkage:-
http://www.importcarparts.co.uk/part...var=0&dc=&gen=