have replaced the cap rotor plugs wires and egr
what will cause an eratic idle and throw a light on 1993 Chevrolet S10
More than likly you have a vacuum leak. The way to locate where would be to get a can of carbuerator cleaner and with the engine running spray around the throttle body and vacuum line and listen for a change in idle.
Would help if you supplied the code attached to the light. Have a parts store attach scanner and hit us back with code.