1996 Sonoma, Vortec engine. Began to run rough, loss of power going up hills, sometimes dies when stopped, generally seems to have less power. We have done a recent tune up, plugs, wires, cap and rotor, fuel and air filters, oil change. I am getting three trouble codes - PO 102 (Mass Airflow Low Freq), PO 340 (Camshaft Position Sensor Circuit), and PO 446 (Evap Canister Vent Blocked). We have had the PO 446 before but haven't gone after it yet. I cleared the codes with and OBD reader but the PO 102 keeps coming back. Is there any maintenance to do on the mass airflow sensor/circuit? Replacement or adjusment or circuit checks? I do hear the fuel pump working but it could be time to replace it too, 140000 miles or so. Any help here would be appreciated. Thanks!
