The Porsche 911 changed from the non-computerized L-Jetronic fuel injection system to the Motronic ML3.1 in 1984. The 911 never ran the model ML1.2 series Motronic. The first version had a 2716 EPROM and only one set of maps. No map switching. The change to a 2732 EPROM, as used in the Porsche 944, allowed the use of a multiple map set configuration. 

Porsche 911
1984 to mid 1986	1987 to late 1987	late 1987 to 1989
For ease of manufacturing, BOSCH went with larger  2764 EPROMs and eliminated internal ROM of the Microcontroller.  It also allowed code changes to the firs half of the code although it appears they never did