I was driving the 93 today for about 10mins and at the first stop light I came to the truck started to idle rougher than it ever has! The rpms are very steady at 600 but the whole truck shakes as though one cylinder is missing. It is also belching white smoke through about 2K rpm when the issue clears up and it run normal. At idle small amounts of smoke can be seen and it smells like oil not coolant. The truck just clicked over 116K and has always been a champ...any ideas?