I have a 2000 Buick Century, 100,000 miles, 3.1 liter engine. The service engine lite is on. I took it to Advanced Auto Parts to get the codes read. They said that the EGR Valve has insufficient flow. I replaced the EGR Valve and per their advice tried to clean out the pipe from the EGR Valve to the exhaust manifold with brake cleaner. But the service engine lite is still on, and their code reader still hits for the EGR Valve having insufficient flow. Any suggestions would be appreciated. The code on their print out is P0401 EGR Flow Insufficient.