It Is probably your ambient air temp sensor. Same thing happened to mine shortly after I bought the car. There is a small hole in the lower grill section on the drivers side that the sensor snap-fits in. The little catch on the sensor may not have enough tension to hold it in the opening. Recommend putting a bead of silicone adhesive round the base of the sensor and just plug it back in the grill. It will work fine. You'll have to remove the under-engine skirt to get at it, though, if you haven't already...