i had my motor rebuilt and when i got it back my check engine light was on. i checked it out and it was those three things. i changed my o2 sensor and it still says it is bad. dont have an ohm meter to check air flow meter but dont have the money to just change it and the problem not be fixed. havent had time to change the knock sensor yet. truck seems as if it is starving for gas when i push the peddle half way. if i put it to the floor or just barely give it gas no problems. if anyone has any ideas of what to check other than the airflow meter since i do not have an ohm meter i would really appreciate it. thanks.