How bad is it to run with only 1 O2 sensor??

[_jb_]

when the car is cold, the lambdas are not used. they begin to be used around 178*, IIRC.

your problem sounds more like an out of calibration ECT or ACT sensor. if it is telling the puter your motor is warm, when the motor is indeed cold, the mixture will be too lean. the sensors can be within spec (no code), but not proper for the situation (as above - telling the motor you are warm when you are cold).
you can check the values of the sensors with a DMM. good luck.

With my truck it's a 94 Dodge Ram 1500 360 and in the winter it really has trouble starting. When it starts it sounds like it's missing really bad, even when a block heater has been running on it. Then I'll be driving and start coasting and my RPMs will drop really low, and will kill sometimes. Another reason why I hate the snow lol.