http://www.ebay.com/itm/Z31-300ZX-Computer-ECU-Non-Turbo-/200755093492?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3ANissan&hash=item2ebdef9ff4&vxp=mtr
here^
i bought one off ebay recently...for much more
i have the same cold start problem, ecu hasnt gotten here yet though...shipping and all that
anyway that should be the one you want, its the worst pictures possible but you can contact the seller to verify