One problem related to ignition has been reported for the 1999 Hyundai Sonata. The most recently reported issues are listed below.
While driving at various speeds vehicle would start to jerk. Would need to downshift to compensate for jerking. Would stall out intermittently. Guages would stop working. Have taken vehicle to dealership, and was informed by mechanic could not locate cause of problem. Mechanic did not test drive vehicle.