How do you know if your fuel injectors are bad in a 1990 Toyota Corolla?

with the car running pull the injector harness off of each inj. if it changes the cars idle then you know that inj. is working - if it doesnt change than that inj is bad with the car running pull the injector harness off of each inj. if it changes the cars idle then you know that inj. is working - if it doesnt change than that inj is bad