1993 Civic 1.6 ltr. Spuddering and lag?

My 1993 civic automatic trans 1.6liter runs fine for 20 minites. Then when you give it gas it spudders and feels like it is misfiring if you only give it alittle gas it accels fine if you give it alot it starts to studder and spudder back off the throttle its ok then the check engine light comes on and the light goes off if you cut the car off then turn it back on when I try to read the code I only get a single bleep in 4 sec. Intervierls. Also where and what does the EGR valve look like and location if that could be the culprit.