First, post this in the eclipse forum, as they would have more specific info then we will, but as far as a vaccuum leak, you can turn the car on, pop the hood, listen for air coming out. If that doesn't work, you can put soapy water on all the connections and such and look for bubbles...when the car is idling.
If that doesn't work, you will need to pressure test it...there are plenty of pressure testers on
www.stealth316.com, or you can check with the dsm guys and see if they have a specific pressure tester method that works best for them. (AS I don't know how similar their intake size is compared to ours.