Mitsubishi Repair: 99 Eclipse wont stay running, eclipse spyder, air leaks

Question
My son, who is Iraq, left me his '99 Eclipse Spyder for safekeeping. I decided to drive it once and it quit running after it warmed up. It continues to do so. I replaced the temp sensor in the thermostat housing but it still quits after it warms up (3-4 minutes). Starts and runs fine until it warms up. I can't even get it to town to a mechanic before it quits. Any ideas?
thanks

Answer
Rick,
I'd first like to say I hope your son returns safely from Iraq, and thank him for serving his country.

For his car problem, he may have a problem with his Fast Idle Air Valve (FIAV).  The FIAV is located in the lower half of the throttle body. It's purpose is to provide additional air when the engine is cold to increase the idle speed and therefore warm up the engine faster. The FIAV is the reason (the only reason) that coolant flows through the throttle body. The way it works is that the coolant flows around a small wax pellet. As the coolant heats up, the wax pellet melts and the valve closes, thus slowly decreasing the amount of extra air let into your engine.

There is an o-ring that makes a seal between the FIAV and the throttle body.  If that seal is broke, excess air can enter the valve; which can cause stalling.  There is also a screw at the bottom of the valve which also regulates air flow.  If that screw is not making a good seal, excess unmeasured air can enter your engine; which will cause it to stall.  

If you have a service manual, some tools, and some confidence in your work, you can dismantle the FIAV yourself and see if you can locate the problem.  But if not, get the car to a mechanic (maybe have it towed), and have them check the Fast Idle Air Valve first, and the surrounding throttle body area for possible air leaks.  My guess is that there is an air leak somewhere in the throttle body area.  Usually an inexpensive fix if it's just an o-ring or seal issue.
Good luck!