Severe overheating can, and is known to warp the heads in these cars. On the other hand if it is idling smooth and isn't overheating then you may have gotten lucky and didn't damage the head. Sounds like you may have a bad alternator or voltage regulator. If your voltage drops significantly then it will affect the engine management system. Check the voltage output of the alternator. You can do this without removing it or have it done for you. Most auto parts stores will do this for free. Checkit at idle and at various rpm's.
