I'm sorry I can't remember who tipped me off to this but it was someone on this board. Anyway, my bird had terrible MPG and terrible HP(4.6). The car was like this for a long time. I did a lot of troubleshooting and a lot of parts changing. The PCM threw no codes. Well, to make a long story short, it was a vacuum leak! I was told to look at a vacuum line buried on the left rear of the intake and there it was, split wide open!! This line is right under the fuel rail crossover line so I never would have seen it without being told to look there. My point is this....thank you to whoever it was that posted pics of this and for everyone else, don't stop chasing the obvious stuff even if you don't see it the first time!!!