I have just went through a month of having my 93 Lumina die several times a day. For reasons unknown when it acted up the check engine light would come on and the speedometer would take a shot toward zero even though the car was still moving at 50+ mph. An experienced mechanic was able to find it by tapping on the ignition module with the engine idleing and this caused it to die. He changed the module and I've driven it a couple hundred miles since with no problems. I just wanted to share this information in the hope it will help someone else.