Poor fuel consumption

Recently my car has been a pain...poor acceleration through 2.5-3.25k revs, i remedied this with a new lambda sensor, however since then my fuel consumption is outrageous, poor idling often cutting out at lights/junctions. When driving engine feels like it's 'backing up' with gasses...i floor the clutch and rev the engine, black smoke bellows out the exhaust! I have removed and cleaned the idle air control sensor...spark plugs seem to fire (though i havent removed and checked them, engine seems a little rough when driving.i have a haynes manual but no idea where else to start. Any suggestions??