My 91 940 turbo wagon bogs down under acceleration, but only after it warms up. Accelerating slowly is no problem, but when it starts straining for more power, it starts skipping & chugging, and black smoke comes out of the exhaust. The only trouble code that shows up is 1-4-3 "front knock sensor absent or faulty." No other codes (other than 1-1-1 when in socket #2) show up. I have left another thread entitled: "cable from relay is unplugged - where does it go?" in which I found a cable from a relay near the drivers side shock column disconnected, but this rough-running problem just started recently and the cable mentioned has been unplugged for a year.

Any advice on what to check is much appreciated!