well all the sudden for the past week my car has been ideling really really really really ruff when i'm stopped, in park drive or what, the rpms get down to the notch before the last one and the car shakes really bad, but it does it in pulses , thats the only way i know how to explain it, it will get really bad then ease up then again really bad, and yesterday driving home my check engine light came on, any ideas? its a 98 4cy auto, just under 98k on it