what may be the issue that might cause a loud idle on a 2003 Mitsubishi eclipse?

Hello, Dave here, contributing to RepairPal and providing expert advice since 2010. I think a physical inspection of the vehicle is necessary for a local technician near you to hear what you are speaking of and address it. It could be an air intake leak for an exhaust leak that is amplified. It is impossible, unfortunately, to be able to accurately weigh in until hearing the noise and getting a sense of it's origin in person. https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.