If it's throwing a CEL, first thing is to pull codes. You can get a basic read in the form of a blinking like on the dash, when you jump the connector under the steering wheel. How-to is in the factory service manual (available via the link in my sig). Not sure how long it stores the code if the light goes back off...

Big Truck: 00, 3.5, Endeavor, 5-Spd drive line in hand!
Little Truck: 87, 2.6T I/C, MT, LSDs, Tonneau Top
Her Truck: 03, 3.8, 20th Anniv, 65k
Daughter's: 06 Eclipse, Keeping it Mitsu!
FSMs: MitsubishiLinks.com