1991 190e 2.3, lambda adjustment and duty cycle

[c55_2005adr]

hi everyone,

i have a 1991 2.3 8v 190e with an automatic, i recently changed the plugs, air filter, cap and rotor...

ive been trying to adjust the air fuel mixture, the previous owner said that it needed to be tuned a little bit because it was running rough at idle. i replaced various hoses that led into the ICV, to manifold and valve cover which did help stabilize the idle. but the idle still is still kind of rough, and when it is put into Drive, the rpms drop to about 550-750 and the motor seems like its going to die. the rpm at idle/park is about 1000.

i have a multimeter that reads duty cycles. i followed the procedures in the shop manual, which includes pressing the buttons on the X92 connector to get it into the "on/off ratio output" (constant light, no blinking and the check light is not on).

so at idle, it is reading a constant 89.9% duty cycle. in the shop manual, it says at idle it should be at 50+/-10%, but if i turn the mixture clockwise, or counterclockwise, the duty cycle at idle is the same. if i rev the motor up, it will move around though.

so my question is, at idle, should the duty cycle move around when i change the air fuel mixture? if it is not moving, would that indicate a fouled oxygen sensor?

thanks in advance!