I admit that I’m in way over my head. I’ve been chasing a rich fuel/air mixture for weeks now and have yet to get a solution. This is the current status as it stands. The car is a 91 300e 2.6 from California. I have been checking duty cycles using voltage readings off the x11 port. In the past the readings after the ecu kicked in would peg at 12.7 volts and not drop at idle or 2500 rpms. I have changed out the ovp, O2 sensor, fuel distributor and throttle position switch. I seem to be getting correct readings from the air flow sensor potentiometer and EHA (but replaced as well). Finally, after doing all this and not getting any change, I went ahead and adjusted the lamba to lean out the mixture. This did lower the numbers to 6.7 to 7 volts, but now instead of holding at these levels, it slowly drops to .09 volts and holds. It will jump up to the higher numbers when rpms are raised, but again drop even as the higher idle is held. O2 sensor gives similar numbers, starting at .84 volts and dropping to .09v. Sometimes, at the leaner settings, the idle will surge and duty cycle will fluctuate back and forth till it settles and again starts to drop. When it does this surging, if I pull the connection to the idle control valve, the surging stops and idle smoothes a bit. With these setting, the car runs but has no power and will bog down at higher rpms.

Does this mean the ecu is bad? And if so, does anyone have an extra one I can borrow to swap out for checking?

In addition, the entire ignition group has been changed, new plugs, cap, rotor, wires and coil.