I've received great tips on this site and now I think I have one to share.

My 2001 VX had what sounded like an exhaust leak, and it was being robbed of power. I had the dealer replace it, but it came back (dealer closed later). I bought one on Ebay to replace it myself. That was easy, but the sound was still there. A friend looked at it and saw that below the mount the EGR mounts to, a pipe fitting had come loose! That's all it was! It wasn't the EGR at all, just a loose pipe connection about 4 inches below the EGR. Now I am amazed at the throttle control I have, and the bad sound is totally gone.

I bought my VX on Ebay, sight unseen, with 56000 miles about 6 years ago. I couldn't have been happier with that transaction. It now has 146,000, with a couple thousand of them over the dirt roads of the Mojave Desert.