1987 760 turbo, my car started smoking due to overfilling the oil. I drained the oil and the smoking diminished greatly, but now it doesn't accelerate properly. It seems to run better with the test plug removed from the exhaust in front of the catalytic converter, but still struggles. It only smokes out the back, but not at the test port, so maybe the cat's plugged up now?

I step on the pedal but it takes a few seconds for it to actually get moving, but is still really slow. It revs perfectly though when in park. Also it sometimes stalls out and stops, and wants to also when put in reverse sometimes. Any ideas?