Unfortunately, Illinois is like most of the other states and "as is" means just that, however it is when you but it is what you get.
The only exception to the "As Is" situation is if the seller made some type of specific, affirmative misrepresentation. For example, if he told you the car "ran good" or was "in good shape" that is not specific enough to be an issue. If, instead, he told you "it has never been in a wreck" when in fact it had, or that "I just got the engine rebuilt last year" when actually the engine had never been rebuilt and the engine had 150k miles on it then it would be actionable.
The amount of work it needs isn't the issue, it is whether there was a specific misrepresentation made to you that induced you to buy the vehicle.
I am truly sorry to give you what I am sure is bad news, but please understand that it would be unfair to you (and very unprofessional of me) to provide you with anything less than a completely honest response. However, if your concerns were not satisfactorily addressed, then please let me know, and I will be happy to clarify my answer. Please remember to rate me based upon whether I answered your question, and not upon whether the answer was good news or bad news since I have no control over whether the law is in your favor or not.