i recently replaced a head gasket and after everything was put back together the car was running rough and has a hard time idling. this goes on for about 20 minutes or so and then begins to smooth out and everything is fine. it only does this when it is cold. Even keeping the engine running is a chore. During start up the engine spits and sputters and eventually dies. Has anyone had this or heard of it before.

 

dirty egr and/or idle air control valve maybe. or not plugged in.