Usually the engine light is signaled when there are emission problems. It could be that one of your sensors is going bad, like the Mass airflow sensor or O2 sensor in the Manifold and exhaust line. If they don't give the computer proper readings then you will not get the proper air/fuel mixture to make the engine operate correctly "irregular idling". The dimming can have a lot to do with the engine not rotating efficniently enough to operate the alternator. Definitley have your Engine Light diagnosed at a place like Advanced Autoparts. | 
