Being able to clear the P1000 code after returning to stock would kind of negate the whole "learning strategy" thing Ford built into the PCM so that it would perform the way Ford wants (to pass emissions "exhaust gas sniffers").
But, I'm going to stick my neck out and "voice" what I think is the "obvious" point that Bill mentioned, since I think it's kind of subtle. If the P1000 code
was set when loading a custom (or canned tune), the PCM would try to bring everything (emissions-wise) back to the stock tune, and it would do that in about 50 miles of driving, negating much of the custom tune.
There are several posters over on f150online who don't see this possibility and have said they don't think custom tunes are worth anything because of the drive cycle, relearn thing. I think Bill has just shown you how they are wrong.
And, I hadn't thought much about this until reading this thread. Thanks for educating an old dog, Bill!
- Jack