A flickering check engine light plus rough idle is usually a misfire or vacuum leak. Read the codes first, then inspect coils, plugs, and PCV hoses.
A rough idle with an intermittently flickering check engine light is often a sign that one or more cylinders are misfiring, but it can also come from an air or fuel imbalance. The flicker is your engine's way of saying the catalytic converter is receiving unburned fuel right now. Before buying anything, pull the diagnostic codes with an OBD-II scanner or have a parts store read them for you.
