what kind of vehicle we talkin here? is it the bmw in your sig? if its a bmw i cant help. btw i loled at the is there antifreeze in the coolant comment. uh there better be lol.
anyways could be a bad coil, can be checked at autozone, dunno if it has a distributer module could be that if it does, autozone can check that. could be a bad roter in the distributer. ect ect