I agree w/rooster. The 03's and Early 04's have the icp in the rear of the engine in the hpop cover. They love to leak and cause crazy idle's. Get on your creeper w/a flashlight and point it up above the trans bellhousing by the top of the Y-pipe. Youll be able to see the sensor and the chrome heat shield-if its leaking oil then get it back before you roll 100k-unless your out of warranty by time(5 yrs).