('01 f-150 sport 4.2L) I just replaced all 4 O2 sensors and now it's running like like crap! It idles low, inconsistent, and often wants to stall (all while idling). I didn't have this problem before I put them in. The check engine light has not come back on yet. The plugs and wires are good. New MAF sensor. Vacuum leak check done recently. I'm not sure were else to look without wasting my time. Do you have any ideas? Any comments are greatly appreciated!! Thanks!

 

what made you replace all 4 o2 sensors ???

 

One of two things happened. You either got a bad O2 sensor (or 4) or they weren't installed correctly. I would double check that the connectors on the front two are on correctly. Either way, if the problem started as soon as you did the swap, don't even waste your time looking for something else like vacuum leaks.