The four Wires are; O2 sensor output, O2 sensor ground, 12 volt heater feed, and heater ground. On 3 wires sensors, the O2 sensor grounds through its case and doesn't require a separate ground wire.
So I think that on the 3 wires O2 sensors it would be enough to find a way to ground the case, using copper strap, to a valve cover bolt and would be quite the same (if you dont wanna buy a 4 wires sensor). It just looks like the 4 wires one has a 12volt heater, which is good cuz it needs to be hot to produce a good signal to the ECU for a good air/fuel mixture... So it makes me think: how about regrounding it to the intake manifold?? What do u think guys??
What else would be good to ground/reground??? I already worked on my MAF and the idle and throttle response is a whole different story.