I have a 94 Lumina APV with the 3.8.I have a problem with a constant electrical pulse that causes all the current in the car to pulse at a steady unchanging pace. It is always present when the car is cold. And at times will disappear completely and run good as the car warms up. But then will come back at random times. Sometimes only for a minute, sometimes it comes back and stays. Also I get a check engine light that will come on occassionally I believe that may be an O2 sensor, If I turn the engine off and restart it goes out if I hit the gas lightly.I have changed to a new alternator, battery, plug wires. New vaccum lines. Checked the connections and plug ins for wire breaks and grounding.I can't determine the issue.I also noticed that the heater duct controls don't work as they should when I am experiencing the pulsing problem.I don't know if that is relavent but I thought I'd throw it in. The van runs excellent except for this issue. Thanks for any ideas you may have.