Q: Getting a P0430 code on my Buick Century 3100.

Hi there. The code p0403 is for the EGR circuit that shows it has malfunctioned. The code p0430 is for the catalytic converter showing that its below threshold. Check the harness to the EGR and make sure that all of the pins are contacting the EGR. Since the EGR valve was replaced, its possible that the wiring has been disrupted and needs to be checked for any breakage to the wiring. Check the catalytic converter and see if the O2 sensors are hook up and functional. If the sensors are working, then the catalytic converter may have failed due to the engine running too rich or too lean before making the catalytic converter overheat. If the catalytic converter is in fact below threshold, then I recommend replacing it. If you need further assistance with your engine stalling around 3,000 rpm’s, then seek out a professional, such as one from Your Mechanic, to help you.