I neeed a smog check for a 1993 ford explorer; however, eng light wont go off!

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I have a 1993 ford exporer sport 4.0 and need a smog check; however, the engine light won't go off. I took it to several smog places. It Diagnosed with codes 214 and 556 (Mass Air filter sensor). I fixed the 556; however, the 214 Cylinder I.D. circuit (system) malfuntion. I was told it is an electrical problem and would cost a lot to fix. What do you think? I want to sell this car.