1997 Volvo 850 Having Trouble Starting, O2 sensor?

[Hale]

My 1997 Volvo 850 Turbo has been having some difficulty starting these past few days.
I bought it about a month ago, replaced the alternator, getting the feeling that this car has been neglected...
Knew it felt weird starting it one day, noticed that it took an extra moment to start up... Then later wouldn't really start at all. After trying again it seemed to start fine. I just still feel this moment of hesitation.
Check engine light came on and my diagnostics told me it was the O2 sensor. Could this possible lack of oxygen reaching the engine be creating my startup problem?

[erikv11]

Usually if the O2 sensor goes bad, you get a code but the car runs fine.

On the other hand, if there is a small vacuum leak somewhere, the car will run a little rough (basically proportional to the size of the leak), and it *may* set an O2 sensor code.

I would check all of the rubber vacuum lines for cracks and crumbles and breaks. Especially the one to the fuel plus dampener on the fuel rail. Unfortunately many of these may be failing because they are 20 years old. I would start by replacing them.

As for the starting problem, I would check into the ECT sensor.

[rspi]