i just got this 1993 FD a few days ago. its having some odd idling issues, electrical issues...

It had an AFC neo hooked up, so i removed that. Also on the passenger side, aside from the actual ecu, is this other box(on the left in the first picture). it also has 2 of these black boxes labled 'control unit'. my roomate here at the house also has a 93 FD and i looked at his ecu and theres only one silver box(the ecu) and one 'control unit'. whats up with this? aftermarket piggyback or something?

the box on the left close up

 

Given the N3A... part number, it's OEM. If you count the number of pins, you should be able find it in the manual. It's bound to be a cruise control unit, ABS or something similar.

http://www.rotaryheads.com/PDF/3rd_gen/

 

ok so its the ec-at control unit. this car was swapped from auto to manual. it still has one of 2 connectors still plugged into it, not sure if its serving any purpose anymore though.

the black control units...ive found that its the air con fan switch control unit...still not sure if im supposed to have 2 of them lol