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

HISSIN50 said:

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.

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