Trouble codes

I have a 2000 ford Taurus 24V and pulled two trouble codes from the computer.173 ( Hego sensor indicates rich condition cylinder bank #1) and code 177 (Sensor indicates rich condition bank #2) .I replaced the upstream and downstream 02 sensor. The check engine light came back on and I pull the same codes. Sometimes the car also stalls at idle. Question #1. Does this car .only have 2 02 sensorsThat is all I could find.Question #2.What is the Hego sensor.Question #3 What could be the problem?

Thanks for any help wth this problem.
Mike

there is 4 o2 sensors 1 on each exaust manifold and im sure 1 before each cat converter(s) if u have 2 converters. I beleive hego stands for heated exaust gas oxygen which would be your o2 sensors if I am right, u prolly replaced the wrong o2 sensors, buy 2 more

Thanks for the info. I will look for the other two, but I sure could not find them.

Check the fuel pressure. Should be around 40 psi with key on and engine off. When engine is running, should drop approximately 10 psi. Since the codes are for running rich, this would be the first place to start.