Ok here is how the emission's go in illinois
1. You go into the emission area, and the put your car on dyno, and run it up to 60mph, and test everying.
2. There is not a visial check at this point.
3. If you pass, then you are on your way, if you fail you have to come back after you get it fixed.
4. You have 2 more chances to get the car fixed and passed.
5. If you have failed 3 times, and you have spent MORE than $450 to try to fix it (so keep all your receipts) then you can get a waivor.
6. Before you get the waivor though, they have the right to look at anything in the car, they can check what they like in the engine.
7. If you move to illinois and have not registered or got your vehical emissions tested, the state has the right to revoke your licence and licence plates.
Any more questions about illinois emissions can be found at the following web site
http://www.epa.state.il.us/