1990 240 DL
Today was btesting out my O2 sensor since I have been having problems with rngine getting too much gas.
Here is why you should avoid cheap parts.
After reading online I discovered that the normal voltage for the sensor is .5 volts or as close as possible to that.

About 1 year ago I had replaced the o2 sensor when my cat convertor was blown. The old one ripped apart when I was attempting to remove it so had to buy a new one. With limited funds I chose to get a universal one from Ebay.
All fine and dandy worked fine spliced it in etc. About 3 months ago went to pull out of stop and car backfired. After that started running poorly sputtering etc.
That began a series of repairs. AMM, ignition module failed, timing belt, fuel pressure regulator. Ran good until warmed up then randomly it runs poorly then ok.
I have parked it for a few weeks giving up in frustration. So today decided to attack it. Put meter on o2 sensor lead. Voltage was .3 approx then rose up to .8 but then it rose to 1.2v which is way out of spec. So just for fun decided to unhook the 2 pin heater connection. Suddenly voltage dropped to .5 volts.
Conclusion that th o2 sensor and the heating element are either shorting or touching inside. So went for a test drive ran perfectly or as normal as it should be. So for now I plan to run without o2 heater. Don't forsee it causing any harm. The point of this is if yours is running poorly, then measure the o2 voltage and if it is not at .5 volt then unhook the 2 pin connector and if it falls to .5v then you know the o2 sensor is bad. Also best to invest in the correct bosch rather than a cheaper one, or at least get one that does not require splicing together wires. Not having the heater might cause a small amount of initial performance loss especially in cold climate but she typically warms up fully in about 5 minutes so I can live with that. What I could not live with was the loading up of fuel especially at idle stopped. Hopefully I can now fix it and enjoy driving it once again.