I just bought a 77 280z and have been going through similar problems. I've found that if the fuel pressure is not correct the car won't run properly. I'm almost there and need to replace the fuel pump check valve. It's not holding the pressure needed and a new check valve should do it. Nissan can't get you one but Bosch has one part # 1583386011. Checker auto or most Bosch suppliers can get you one. I'm hoping when I get my new check valve on Wednesday all my problems will be solved. This part is less then $30.00 and could solve the problem. I hope this is your solve as well.