I have a "never there when you need it" problem - "never there" because it never shows when my mechanic has the jeep - 2012 Liberty - usually idles at 550 or so, on warm engine when sitting for a while idle sometimes but not always climbs to ~800 and it idles rough . . . let it sit long enough the MIL light goes on . . . and a few days later the light goes off . . . always showing a misfire on cyl. 5. Over 5,000 miles I have added about a 1/2 gallon of coolant . . . no visible leaks beneath the car. No overheating.