i have a 2002, f350 , 7.3l diesel , 6 speed , 4 wheel drive , when driving or parked with the engine running, the emmisions light comes on and the engine dies immediatly, to get started again i have to wait a bit, the i turn the key to on then off, several times, then it will start, sometimes it will do it several times a day, some times it will go for days without doing it, this truck is used hard as a working farm truck, with right at 100,000 miles, i do regular maintenance on it, can any one tell me what is causing this and how to fix it.