Well I got the new coolant sensor and O2 sensor in my 87 745T last night.
It might be one for Steve to update the FAQ's for. I did a quick look for my original post and couldn't find it. (Lazy) But to bring you up to speed my engine would go from normal to full rich at a drop of a dime. Poor running and lots of black smoke at idle and under power. Or should I say what power it was making it was marginal at best even under boost. Worst part it would come and go and especially go away just before you took it in to the shop to find the problem. Well it went full rich all the time Wednesday and I finally pinned it down to a bad coolant sensor. Well what was driving me nuts was there was two stages of poor running, bad and worse. Bad was when the coolant sensor went south. Worse was when the carbon built up around the O2 sensor from the rich running engine. Other then the feel from driving the car my boost gauge would show slightly lower vacuum. It would sit at 9:15-9:30. When it went to worse the gauge really lost vacuum and rise to the 10:30-11:00 area.
If I ran the rpms up to 5-6K under boost it would clean off the carbon that was accumulated on the O2 sensor. It would then run better for a 1/2 hour or so and go to the worst stage again. The coolant sensor was making it look like the O2 sensor was the problem and vise versa. Replaced both and problem gone. Vacuum gauge is sitting at 8:30 at idle with the clutch disengaged.