EGR Replacement = Engine light out then on next morning

egr sounds like it was your code, but there are 2 passages that are at the egr valve. one for exhaust and one for vaccuum. the vaccuum one tebds to clogg up at throttle body and the valve will not function properly. you need to remove the valve and start up the motor and see if you have an exhaust leak and vaccuum. Roy

Here Is a Solution to the EGR problem on the 3.1 Chevrolet Engine......After I removed the air cleaner and air intake tube passage to the throttle body and the EGR valve I ran a wire thru the passage to the Throttle body from the EGR base in the Manifold.The passage was clogged with carbon. A plug came out. I then sprayed the open throttle body passage with carburetor cleaner and wiped all the dirt and carbon from the Throttle Body. I then reassembled the removed parts and cleared the Codes. The car then was driven for 5 days without any codes being thrown and it went thru NJ Inspection with flying Colors. By cleaning the Passage in this manner I saved a lot of money and time, making a bad problem easily solvable.Use caution when cleaning the Throttle Body that you get ALL THE CRAP OUT!!