cant get lambda to stay in adj.
 

I have an 84 500 SEL The o2 was original so I replaced it due to pore economy, and replaced the fuel distributer due to it leaking fuel from the regulating piston. I checked the lambda on/off ratio after warm up it was around 87% exhaust was smelling rich. I adj. it down to 60% but it would just go back to 80+% If I hold the idle at 2500 RPM lambda will creep up to 90% then settle back and fluctuate between 78-89%. I am checking this with a crafstman meter that measures cycles. I checked the voltage at the O2 sensor it was about .80 volts while I was observing 78-89%. The engine idles rough. I assumed the fuel distributer (a rebuild) was bad so I sent it back for another, and the same problem exist with on change. I have sprayed the intake manifold with brakclean to detect vacuum leaks but nothing indicated. I would very much appreciate any sugestions anyone may have.
THANKS
MACKLTRIDER