rough idle

i have a 1994 grandam with a HO quad 4 when cold it runs fine but when it get warm it misses a lot. also when in gear and i open it up ahlf way it stumbles and misses reallly bad then i give it less gas it runs fine. but when the engin is cold it runs fine i am truly stumped thanks

i have a 1994 grandam with a HO quad 4 when cold it runs fine but when it get warm it misses a lot. also when in gear and i open it up ahlf way it stumbles and misses reallly bad then i give it less gas it runs fine. but when the engin is cold it runs fine i am truly stumped thanks
You have a egr valve that is bad .have it scanned at a shop they will tell you that.