Euro 126 '82 500 SEL CIS engine; 0 pollution controls (no EGR; no cats); put new Oxygen sensors; fresh Mobil 1 W 20-40 (temps are warm out here) adjusted mixture to lean it after a mechanic fooled with adjustment. Ran smooth and nice while weather was warm; now (cold spell) is running very rich again; lots of black smoke under acceleration; had plugs out (new Bosch WDC9) all had lots of black carbon; cleaned them out; car idles good at 6-700 RPM's but still has some engine shaking. Notice one plug wire is disconnected out of a line plug that runs into fuel distributor; when plugged in smooth idle goes south. All vacuum lines connected. Any suggestions would be appreciated.