While I agree with the suggestions to camp well outside the city and take the train in, you said that you only had 4 hours to spend downtown. The train ride is going to take 2 hours of that 4 hours.
If you truly only have 4 hours to spend downtown then the only option in my opinion is to use the McCormick Place marshalling yard as a parking spot and then either use the L trains or Uber to get around to some sites.
It's going to be very difficult to spend 4 hours downtown and still get in and out of town without some significant traffic. Your only real chance is to target 10 a.m. to 2 p.m. as your time downtown.
You would also need to call ahead to make sure that there's no significant events at McCormick Place in case they will not let you in the marshalling yard.
After leaving there for the day then I would head west on 80, not 88, and get out to Joliet or LaSalle or some of those towns in that area