John
Unless your flywheel for some reason is incorrectly installed [which is highly unlikely] Or your crank timing gear has slipped on the crank shaft [broken or worn tang from incorrect torque] there is no mechanical or electronic reason for your bsse idle timing to be off, at least not with the information you have given us so far [ie; the outer crank pully has not slipped]
The BASE IDLE TIMING is not modified by the computer to my knowledge. It is only above idle that it is advanced or retarded. For that reason it is seldom found in publications except to say that is not adjustable.
That is why I suggested checking that the timing does advance with increasing rpm as a means of guaging the operation of the computer and related sensors. The timing should begin to advance at about 1100 to 1200rpm and max out at 2000 to 2200 rpm. The two things that modify this action above idle are the knock sensor [which will retard the advance above idle when it senses knocking] and rapid deceleration [which will hold this advance longer during this deceleration to smooth out this transition and reduce emissions].


rjc