Buick Roadmaster EGR problem
 

I recently bought a 96 Roadmaster. Drove it back from Florida to Pa. with no problem, engine service light on. In order to pass Pa. emissions, my mechanic had to clear the codes, found the EGR was unplugged. Now the light is off, but car sputters after warmed up; replaced EGR valve, but still sputters, surges; replaced the EGR solenoid valve, still same situation. Error code was 403. Now my mechanic says he has no idea? Help! , anyone ever had this problem. Car ran fine before he cleared the error code with the EGR uplugged.