Ford F150 V8 302 5.0L EFI

I posted a message back on March 25, 2003 on this topic (http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=ford+steventhomas42+picky ),
and was glad to receive two diagrams from Tony (Thanks Tony) to help out.
Unfortunately, we still have unanswered questions. For those of you who have access to Mitchell's, if you look at Fig. 3 $ 4 of the 5.0L V8 diagrams (200818 & 200819), both illustrations show two vaccuum lines from the canister, one "to fuel tank" and one to the T.B.I.
My truck has a third (white) vacuum line that is at this point unattached. Does anyone have an idea where this unidentified line is SUPPOSED to go?
The turck idles rough, the Oil Pressure wavers while idling, and the check engine light comes on. I believe these are all related, and hope that sealing this vacuum question will solve them.
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