why is my 1990 deville idling high at start up and then idling itself down after

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Got code e-49...cleaned throttle body and checked the hoses from the egr valves no leaks. car ran good for two months. now the problem is back.checked codes and e-49 came up again. I cleared the codes and got0.9.0 then 7.0..now when I drive it seems like I have the cruise control on. it will hold the speed of 30mph and i don't even have my foot on the gas. should i replace the diverter valve and the egr valve?