The problem is that you can't run rich and "run". The system is self regulating so you aren't.
With a new O2 sensor its possible to correct a system that someone just overwhelmed with ignorance but your car will not run rich in closed loop. To get to the bottom of this you must establish closed loop. Check the archives for more on the concept and look at the DIY article evaluating engine controls to see easy methods for analysis.
Bosch Master, ASE Master, L1
33 years MB technician