It sounds like a heater core that is bad. If that is the case then you can't do any thing but wait. Unless you now how to replace the core, to make sure it the core, do you smell any thing sweet or do you see antifreeze on the floor? If so that is your core leaking.
Okay I read the owners manual about using 87 or 89 in this car. I just want to make sure it's okay from maybe people who have already tried this out. I have been use the 89 every since I bought the car. So being that I am a little tight on money I am looking at all angles as for cut backs.