Code 11 is a momentary interuption in power to the ecu computer
says to check
ignition switch
ignition switch circuit
main relay circuit
main relay
check the ecu
here the page
http://www.supra.co.nz/87tsrm/EFI/efi30.htm
something is loosing power ? disconect the ground wire for 2-3 mins and reconect to clear codes and see if it trips the code again? check your batt cables and the main ignition wire off the batt,
check your grounds too some gm cars a code 11 is no codes pressent but i am not sure on this one..