what could be the problem?

I took out my new plugs and saw it was running rich (sooty black) also my lil civic is drinkin gas (22mpg).... I dunno whats wrong. I recently replaced the cap, rotor, ignition coil and plugs. No CELs, tire pressure fine, no dragging brakes.... what could be the problem? to my knowledge the A/F mixture is controlled by the ECU...... what sensors controll it too?

help!

*update* it seems to get good gas mileage this tank... but that means it a speratic problem and I want to fix it before it starts to suck gas again...