Rough idle and bad gas mpg on a 93 deville

Just bought a 93 deville with 132k , I am trying to get it running perfect. Already performed the complete tune up with wires cap rotor ignition module, timmed , cleaned the throttle blades front and back. checked egr , cleaned the egr tubes, I get a slight miss on idle that I cant get rid of. Checked all vacumm lines , cant find a leak, sprayed intake with ether , no change . Thinking it was the ICS and tbs not set right but cant keep the car running with the ICS retracted. What do you suggest? NO codes, all switches work.:banghead: