probably a bad grounding somewhere...check if your ground on the thermostat housing is secure and tight (I circled on the diagram, located behind the Distributor)...I had same issue as yours, and found this was my problem the bolt was loose..but if not ur case, then bust out voltmeter, and start checking. ALSO, check if timing belt has not snapped, missing a teeth, or loose (if loose, tighten it up via tensioner pulley)!!!