Last year I had the code p0133. I replaced the upstream o2 sensor and this did nothing for the code the sensor was $90 at the time. I took the car to a shop and the mechanic said it was a leak between the throttle TB and the MAF. He coated the intake box with a thick layer of grease were the TB meets the intake box. We had no code for about 8 mounts. Then it came back. I would push the intake down hard and it would go away for 1-14 days. So I figured it was the intake tubing. I bought the custom air intake tubing from the auto parts store and the code was gone for 4 days. Now the codes comes back almost every time I run the car . The hose clamps are tight as can be. Whats the deal? The car get terrible mileage when p0133 is tripped. I love this car and I don't want it to be messed up.

 

There are times when an aftertmarket O2 sensor will not perform as expected.
Do you know if the O2 sensor was purchased from Ford or not?

 

....and there could be other vacuum leaks. The PCV hose or the brake boost hose or any other vacuum line could be leaking.

 

It did not come from Ford.