Without the O2 sensor, the ECU goes into open loop mode.
Did you separate the heater ground from the sensor ground? Having them together can affect the O2 signal
(especially if your power source for the heater is on the coil, since the voltage will vary with the ignition) This variance will make it to the heater ground wire, and will overwhelm the O2 sensor signal output if it's grounded with the heater ground. (the sensor ground will vary up and down by as much as 100 milliamps, which will cause the O2 sensor signal to vary that much; which will confuse the ECU if the output voltage goes up or down when it's expecting down and up)
