2001,EGR code, Cylinder 4 misfire code 0304 detected.

In the winter I sometimes got an EGR code then it would go away. Replaced the EGR valve with cheap China one now getting Cylinder 4 misfire. I got a slightly used supposedly known good one from eBay (looks decent) same 304 code. If I block off the EGR tube 304 code goes away but get EGR code. I changed the ECT and IAT sensors thinking the ECM does not know the engine is warm and may be keeping the EGR open. What could be causing this? Head gasket? I know the EGR takes from cylinder 4 in this engine, should the EGR fully close when the engine is warm or does it stay slightly open all the time?