I drove it around the whole day no problems. I stopped off at the auto part store for something. I got into my Mark VIII and turned it on. It started to tremble. It is getting worse. I changed the sparkplugs immediately thinking that would solve the problem. No good. I checked the coils and they are good. The fuel pump was changed 8 months ago. It has relatively new wires. It trembles then dies. Could it be the crank sensor or timing sensor? Thanks for your help!