If your egr tube has a crack it will cause a very rough idle due to vacuum leak. Spraying the tube with carburetor cleaner while the engine is running will cause the idle to smooth out if you have a leak. They soapy water will show you wher the leak is. I tried high temp silicone sealant but it only helped for a few days. I took the tube to a shop to have it brazed but they were concerned that they would burn a bigger hole. I finally decided to try brazing it myself. I had never welded anything before but I was able to pull it off. So it is possible but I would reccomend finding a shop that can do it as there is the riks of fire, and serious injury. Also, I have found several egr tubes at the junkyard but they have all had micro cracks so far.
1995 Bonneville SSEI
1994 Buick Park Avenue