Ther is your problem right there. Nissans will NOT run very well...if at all with the Engine coolant Temp sensor not connected. check the connector, and make sure it is on tight. if it still throws code 13 then go get a new Engine coolant temp sensor (2 pin) from the dealer. make sure to tell them its for the ECU not for the guage cluster. the motor has 2 sensors, one small single pin fo rthe guage cluster, one 2 pin sensor with a clip liek a fuel injector. they will both be located right near the thermostat housing.

Scott