my 96 thunderbird gradually idles up to about 2000 rpm's can u help?

i have replaced nearly everything i know to replace.changed idle control,temp control,tps,vacum canister,maf sensor, the oxygen sensor i coulnt get off but i pluged another one on it and laid it on the exhaust.the check engine light was on.it was the temp.sensor and now no codes but still i start the car and it idles about 1200 then after a minute drops to 1000 then gradually idles up to about 2000-2500 rpm's.other than the idle problem it runs great.i did replace most the parts with ones from junkyard.i wanna fix this car and give to my mother,please help