Hey folks just picked up an 87 GN with about 40k Miles on it. Been sitting a bit. Starts reasonable well. Idles well but high for about 45 seconds then drop really low and eventually stalls. Changed plugs and wires and just today added new air intake with MAF translater. Figured that might help but still doing same. While under hood added a manual boost control. And now Service engine soon light on but was not on before. Guidance anyone?