will a bad 02 sensor cause my jeep not to start or cause it to flood? most of the time it starts up fine and runs fine but sometimes like today it started fine and i drove it for about 20 minutes and then it wouldnt start back

 

Yes. But unfortunely so will a few other things. Fortunely O2 sensors are easy to test.

 

the o2 sensor is bad i tested it

 

Can you give us some more details...? A 1984 XJ with the 2.8 V6 will flood if the carb is out of whack and has an O2 sensor, sensor has nothing to do with it...

 

its a 96 and it has done this 2 or three times but it runs fine after starting and sometimes it wont start unless i step on the gas pedal. could it be a bad fuel injector?

 

I think what salad is trying to say is, year and engine size would be of much help. The only info I can see is that you have an XJ with a bad O2 sensor and some other issues.

 

96 4.0 h.o.

 

No. It does not take input from the O2 sensor during starting/warm-up (aka open-loop). Check fuel pressure.

 

Okay a 96 4.0L, with Chrysler OBD-2! So it actually does flood then? Or are you just using that to describe "doesn't work"?

Check your fuel pressure, check the TPS with an analog multimeter (a few writeups on that subject exist here already), and check your IAC. I recommend popping off the entire throttle body and cleaning everything with a toothbrush and some throttle body cleaner. Gaskets reusable if they aren't damaged. Don't mess with the IAC's pintle as it is delicate. I can't remember if 96 had a firewall-mounted MAP with a little vacuum hose or if it's bolted to the throttle body. The vacuum should be checked. There is also a test that can be done on it to see if it's failed.

Even in open loop (long after the engine's been running like belvedere said) the O2's contribution isn't significant enough to mess with things that much. The TPS and MAP sensor are though, and your IAC could be sticking.