I'll give it a shot disconnecting the O2 sensor - it should run richer than normal that way, correct?
Not necessarily----this is a common misconception about oxygen sensor-equipped cars of this era, that open loop is somehow "richer" and/or the ECU uses a completely different injection map than in closed loop mode. Neither of these conceptions are true, and I will attempt to explain why.
"Open loop" means that the system is ignoring the voltage signal generated by the oxygen sensor. In these Alfas and other Bosch EFI cars of this era, this only occurs under two conditions. The first is before the engine has reached full operating temperature (because the engine needs a richer air/fuel mixture due to fuel condensation, etc, and the oxygen sensor takes a while to warm up, especially in the early cars with non-heated O2 sensors). The second open loop condition is if the full-load contact of the throttle switch is closed; the base injection map is tuned to have a richer A/F mixture in this region to control combustion chamber temps and stave off detonation, and if closed loop feedback were allowed in this high-load region, the engine would likely hesitate and surge as the system attempted to drive the mixture lean. Well, there is a third way to achieve open loop, and that is by unplugging the O2 sensor
If your engine is perfectly tuned and has no vacuum leaks and all of the injection system components are in spec, unplugging the O2 sensor will not make a drastic difference in how the engine runs---the injection map is tuned to provide near-stoichiometric A/F ratios during idle and light load/cruise conditions anyway. The early single-wire cars tend to hunt a tiny bit at idle while in closed-loop mode, as the nature of the oxygen sensor composition is designed to alternately drive the system lean and rich in a sine-wave pattern to allow the three-way catalytic converter to achieve maximum effectiveness (lean to quell HC and CO emissions, then rich to reduce NOx, while averaging 14.7:1). Later Bosch systems have more advanced oxygen sensors and engine management and idle control valves to allow a smooth idle while doing the same.
Anyway, if your engine has vacuum leaks or anything else causing a general lean running trend, it will run leaner if you unplug the O2 sensor (vacuum leaks tend to be most prominent at idle/low engine speeds). Likewise, a dripping injector(s) or anything causing a rich condition will do the opposite. The oxygen sensors of this era tend to bias towards the rich side if/when they degrade, which is often only noticed during a state emissions test. Occasionally a sensor will be shorted or very far out of range, causing more extreme running issues, but I doubt this is the case based on your description.
Sorry for the long-winded explanation, but I hope that it clears up a few misconceptions!