The elbow had rotted out and was sucking in air. Its right under the throttle body. Heat eventually got to it because its a cheap japan crappy part.... if you hear a whistling noise it might be but you will have to look for it.

 

My wife's 99 just popped the p0171 code this past weekend. I opened the hood today and I can hear a definate sucking sound comming from the center top of the enngine, could it be the same elbow?

Where do I find it?

Other than brakes this will be the first work I have had to do to her truck, great vehicle...

 

just follow your intake tube up to a silver tube( throttle body) you will then see hoses running into the intake around there. Check these hoses for air leaks. Good luck; that is not a fun code throw.

 

Old Grey Ford

It is the same elbow, the one comming straight down out of the throttle body, I can grab it and bend it and the sucking sound fades.

Did you say this was a dealer item? where does the other end go to?

 

Yes its a dealer item AutoMorons and other places dont carry it. It was only $10 and it was the only one our dealer had here.