I have a completely stock 2000 ls that runs ridiculously rich. it always ran a lil rich since i bought it but now its too much, half a tank in a day or two. Ive changed the oil nd filter nd spark plugs. Replaced ECT nd unplug the O2 sensor hopin it wuz bad, nd that the ecu would run off preset measurements. But its still runnin rich, please help. Im goin broke dumpin $$$ into the tank.