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My 1990 F250 129K has developed a rough Idle. I did the standard tune up (plugs, wires, cap rotor, air filter) Fuel filter was done 03/09 and I have 40psi fuel pressure. No CEL but I get a code 12 (unable to maintain idle during self test). I do sense a rich runing smell during idle. I was thinking EGR Valve but I hate throwing parts at the thing. Seems to run OK at speed, but I have not had it on the road, just up and down the long driveway. When I first start it cold it will die with out throttle, once warmed up I have the bad idle. Go to WOT and let off usually will die with out throttle help.