SOMETIMES RUN TOO RICH

[JOROGO302]

MY 1993 240SX RUNS INCREDIBLY RICH SOMETIMES AND STALLS . THIS CAN HAPPEN AT IDLE OR CRUISING. THEN IT SUDDENLY RUNS PERFECT! WHEN STALLING THERE'S A LOT OF BLACK SMOKE COMING FROM THE TAILPIPE . I PERFORMED A COMPLETE TUNE UP:I CHANGED SPARK PLUGS, ROTOR,CAP AND WIRES, ALL GENUINE NISSAN. BUT NOTHING HAPPENED. ALSO I CHANGED THE COOLANT TEMPERATURE SENSOR , CLEANED UP IT'S CONNECTOR BUT AGAIN, NO LUCK. AFTER THAT I CHANGED THE O2 SENSOR (BOSCH), AND AGAIN, NO LUCK. WHEN IT DOES THE MISFIRING AT HIGHWAY SPEEDS (CRUISING @ 55 0R 65) YOU HIT THE GAS PEDAL TO THE FLOOR AND MISFIRES RITHMICALLY TWO OR THREE TIMES AND THE REVS UP. IT HAS MANUAL transmission AND HAS OVER 160,000 MILES ON THE SPEEDO. IT DOES NOT OVERHEAT . I CHECK THE GROUND WIRES AND ARE BELOW 2 OMHS. ANY IDEA? IT IS COMPLETELY STOCK EXCEPT FOR THE K&N AIR FILTER.