Driving at any speed warm or cold, for years, the incident of ignition cut-out was very infrequent and the engine restarted with no problems immediately after turning the key switch off, then turning it on again and starting. I could do this while coasting by shifting to neutral and continue without losing much speed. Now, in the last week it has become much more frequent, every day or so. What's going on? How can I trouble shoot this?