rdwanjr

After 100 miles or so of 80 mile an hour driving my 2001 S500 [W220] starts using much more fuel than normal & runs rough at idle. When I hook up the OBD Reader it shows that the fuel trim is too high which is to say the ECU is making the fuel mixture too rich. When this happens the oxygen sensors appear to be nonoperational: putting out zero voltage. But the O2 sensors are brand-new and the output from each of the four says zero. And after a day or two everything gets back to normal. Each of the sensors puts out normal voltage, fuel trim is right where it should be and the car purrs like a kitten.
Presuming that the O2 sensors are working properly it would seem that the ECU is either not receiving or not recognizing the voltage from the O2 sensors.
Is there any possibility of a bad connection? Or is the ECU bad?
I see a lot of companies offering to refurbish or repair or rebuild ECUs for roughly $200 to $500. Removal and reinstallation takes about five minutes and they claim their turnaround is a couple of days. Does it make sense to try this?
Any thoughts?
Thanks in advance,
Richard