[Thorleif]

I have an 1982 930 with SC cams and a twin turbo system. # 4 spark plug is covered in black soot, and after cleaning it, 3 - 4 miles of driving causes it to be covered again. I swapped out the spark plug, distributor cap, rotor and plug wire as well as the fuel injector. No change. The other 5 plugs are fine. The compression is even on all cylinders. Can the problem be in the mixture control unit? Any suggestions? (I have a little bit of oil spread in the intercooler due to a turbo scavenge pump issue, but that has been fixed.)Thanks Thor