My son is driving an 87 740GLE turbo wagon that I purchased as a first car for him. It was in rough shape after sitting in a tow yard for over a year. Initially it was getting 24 mpg but the turbo was not working. I found a loose rod or something underneath the turbo and connected it which activated the turbo. The fuel economy dropped immediately to 15-16 mpg and there was a loud roar from the manifold. I have looked for vacum leaks and can't find any. The fuel economy drop was dramatic and followed the connection of the turbo. Thanks in advance for any suggestions. My son does not have a lead foot and his driving habits did not change.