RPMs varying - 1998 Jetta

I've got a problem and I hope someone can help. I just recently had my clutched replaced and after I got it back I noticed that the idle RPMs is considerably lower that it used to be. It used to lock in at 900 RPM. Now it hangs out around 400 - 600. Also, it doesn't just stay at one RPM but varies between 400 and 600 every few seconds. I ran the codes and it came back with P1582 (Manf Cntrl Veh. Spd, Idle Speed Control, Auxiliary Inputs) and P0506 (Idle Control System, RPM low).

Can anyone help me understand what this means in terms of some component I can replace or adjustment I need to make? Thanks a bunch. Ray

Sounds like the throttle body might not be functioning correctly. Also they might have forgot to hook up some sensors and vacuum lines arround the transmission.