Fuel system question

While i had my 95 GT in my automechanics class shop i tested the fuel pressure and got 20 psi with KOEO. Then i got 30 psi KOER. I know the specs are 35-45 psi KOEO and 30-45 psi KOER. Would a bad regulator cause the KOEO reading? I forgot to pull the vacuum line when the engine was on to se what the pressure went up to. Also acouple times when i shut the engine off the fuel pressure would drop to 0. Sometimes it would stay at 20. Whats the deal with that? Also would 30 PSI cause a lean condition? Because thats how the car is running