98 Sunfire gt 2.4l

I have had a prob with my car sounding as if its about to stall and missfiring on #2+3 cylinders its been happening for quite a while only seems to be happening in idle.I tryed to replace egr valve(made no difference) had the throttle bodie + injectors cleand out all fluids have been changes all filters changed (no difference) somtimes its worse than others and it also seems to dissapear at times expecially when I take it to the mechanic anyone have this prob b4? Any suggestions the engine check light comes on somtimes when its really bad to let me know its had a missfire according to my code reader.