I just bought my first Ford Truck (98 F-150 supercab lariat 5.4L). The check engine light came on, so I had my friend hook up his snap-on computer to see why. He said that my drivers side front O2 sensor is bad and that he could make the light go out, but it would come back on. The light went out the next day and still has not come back on. The light has come on and off several times since I bought the truck (3 weeks ago). He said not to put in an aftermarket O2 sensor as they are crap and to spend the extra $$$ and by Ford. I had this same problem with my prior 92 GMC Jimmy and bought aftermarket and it ran like crap, so I had to go with original GM O2 sensor and it ran fine after that. Does anyone have any feedback on O2 sensors (Aftermarket or OEM). The check engne light has not come back on, but I know its just a matter of time as the truck has 63K miles on it. My friend also said that once you change one O2 sensor that the other side (front) will probably soon follow. I still seem to get 15MPG and the truck only runs rough every now & then at stop signs.

 

My truck is a 98 4.6...It was idling poorly too (@~40,000 miles). So I replaced the O2 sensor before the cat. ($50 Bosch at Autozone). It worked fine.

Unfortunately 2,000 miles later, the truck just wouldn't start.
It would run only with your foot on the gas. It had nothing to do with the O2 sensor, turns out it was the idle air control valve. It cost me $192 at the dealer to have it replaced...I'm still trying to get them to pay for it since they've admitted the old valve was a design problem. The new valve should never have issues.

See what you can do...maybe the dealership will work with you.

 

I'd say go with the aftermarket and save your money. I think most O2 sensors are made by Bosch so they should be fairly reliable.