1996 Chevy Blazer Check Engine Light

Over the past 6 months my check engine light has began to click on and then off. Sometimes it stays on for only a few seconds and sometimes it stays on for a while. My father has done a tune up on it and still the light is on. When he uses a machine it tells him there is a multi-skip. I am trying to sell my car and do not know what is wrong with it. My father has is own business working on cars, and said that there are a number of things that could make the light act the way it is. I do not want to spend a lot of money trying to fix the car just to sell it. What could cause this problem?