my brick (91 940gle, 16v) has been running fine and getting ~21 local and ~26mph highway, the idle seems unstable especially at start up, red light, check the o2 sensor output, taped off the green sensor wire (still connected to engine) and get reading up and down from 0.03 to 0.8.. volt, the engine tends to "shake" when the idle was low and the reading fluctuated to a lower reading, am i suppose to see a rather steady reading, also checked reading when artifically created a small vac leak at the intake (per FAQ), the reading went down to below 0 volt and stayed around -0.02 to 0.03 for a secon or two, and then back up to between 0.03 to 0.8.. volt and then started to go up and dowm again, the AMM does not seems to have any adjustment screw, how and should i check the AMM, or the 02 sensor is the problem, TIA...

91 940gle 16, 92k (lots of local and short drivings before)