I have a 94 Grand Prix SE 3.1 with 195,000 miles. The check engine light comes on indicating #3 EGR valve problem. I am getting a shudder under load. Just wondering if this is an oxygen sensor problem or otherwise? The EGR has been an ongoing issue, but has never caused shudder before. It has never caused a problem with the way it runs, just the service engine light. Any insight will be greatly appreciated.