91 SC running rich

My fiancee has a 91 sc dohc that has given the 45 trouble code. I know this means that it is running rich, but how do I go about fixing this without putting a ton of money into it. It also will idle really low at times and then when you drive it, it tends to drive itself. After you drive it for say 15 minutes, it will die and won't start again for a few hours. Also, when you come to a stop it is really jerky. Any help would be appreciated.

Chris

45. Oxygen sensor indicates system rich

frist if you have never replaced the ECT, do it and use the new brass-tipped style from Saturn. then check your intake for resiction or a dirty air filter. and remove the O2 sensor and check it for carbon build-up.