I have an '89 760 that has been having problems shifting gears above 2nd. It also is running rough at higher speeds and is blowing black smoke. I found a few posts regarding these symptoms, and it possibly could be caused by a leak between the turbo output and the intake manifold. I have given the air hoses a brief inspection while the car was idling and couldn't detect any leaks. I assume that the turbo is in bypass at idle so the pressure from the turbo won't be very high, making a leak harder to find. I might add that the shifting problem only starts after running for about 5 minutes, the first few shift cycles are good. I checked the kickdown cable and it appears to be properly adjusted. Do these symptoms sound like an air leak, and is there any particular place that I should be looking for a leak? If the intercooler has a leak, how would I detect it?