I just bought a 1990 740 i/c turbo wagon last weak and it performs poorly under boost. The guage goes almost half way up in the the yellow, but it is down on power for sure. It will barely accelerate at WOT at 80 mph. I changed the oil, spark plugs (looked fine but were platnium), and air filter (was pretty dirty) and the problem persists. There was oil in the intercooler plumbling as well as a few ounces in the bottom of the intercooler itself. I also replaced most of the vacuum lines with new to no avail.

I am going to verify fuel pressure with a gauge and try unbolting the exhaust at the cat to check if it a back pressure problem. Any other ideas?

Thanks,
Shap