I have had a fan problem with my 88 IROC also. There are two fan relays on the inner edge of the fender right behind the battery, like an oval shaped cylinder about 3" long. They are likely to fail, as is the temp sensor in the head or intake. Did they come on at one time, but dont anymore? They typically dont come on till the engine is really hot, about 220 degrees or so. the terminals on those relays also corrode, so make sure they're clean.