My friend owns a 2003 Mitsubishi Mirage and it will not idle at all. It starts and will run about 5 seconds and turn off, but if you slightly press the gas it will run fine. We did a complete tune up, including fuel filter, checked for vac leaks, but still does it. A mechanic says it will cost $500 to fix it, but i am sure it is something simple that i can fix and save my friend some cash. There check engine light never comes on, so there are no codes stored in the computer.

 

Check for vacuum leaks! i would recomed to get a can of carb cleaner and start hunting for your leak. If you don't know how to do this pm me

 

Also im not sure what motor is in the mirage if it is not an EVO but check if there is an ISC or something similar that you can adjust. More than likely though you have a vacuum leak.