A MD80's AHRS malfunctioned after takeoff and when the aircraft did not fly the vector heading ATC notified them of a 15 degree error. After correcting the heading error; systems returned to normal. No abnormal system errors or popped circuit breakers were found.

Narrative

We departed on a SID. Captain was pilot flying; I was pilot monitoring. Takeoff was normal. Upon selecting 'heading select' to turn to a 180 heading; the flight directors failed. The Captain continued to fly the procedure raw data while I monitored and tried to reinstate the flight directors. I also had to reinstate the packs from a 'packs off' takeoff and ensure normal pressurization. It was a busy departure. Departure Control assigned us 6;000 FT and heading 360. Once established on this heading; ATC requested we state our heading. We replied '360' and the Controller replied we were heading 345. We compared compass displays and noticed a split. I checked the wet compass and the Captain checked the standby and GPS to determine which was accurate. We notified ATC of a heading problem and turned 15 degrees right. There were no alerts; flags; popped circuit breakers; or applicable QRH procedure. I manually corrected the headings with the AHRS compass controller on the overhead panel. The compasses were now fine; but we still had no flight directors or autopilot. Once assigned direct on course and upon selecting NAV on the Flight Guidance Panel the flight directors returned and the autopilot was usable. ATC made no mention of the heading correction and handed us off. The compasses; Flight Guidance Panel; and autopilot functioned normally for the duration of the flight.