If adding fuel down the airflow meter affects the starting condition, then it is likely that you do not have fuel pressure. Having the pumps running is not enough.
Without a pressure gauge this is hard to test. Only way I can think of would be to pull one injector, leaving the fuel line connected. Jump the fuel pump relay (make the pump run) and depress the airflow plate. Fuel should spray from the nozzle. The injectors have an openning pressure about 50psi and will not spray if that isn't reached. This is not very quantitative as the system pressure is much higher than this and must be stable to work properly.
Bosch Master, ASE Master, L1
33 years MB technician