My 99 Chevy with a 4.3 v6 runs rough with mass air flow unplugged and just about wont run at all with mass air flow plugged in. Replaced mass airflow but nothing changed. Used wiring diagram and tested for proper voltage and ground at conector also signal voltage at conector. Have had problems in past with distributor. Recent replaced whole distributor, cap, and rotor. Have no idea were to go with it now

 

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