engine shutters ???
 

01 f150 some times when setting in park it flutters a little. I don't notice a miss when I rev it up a little. I do need to change the plugs i'm sure. but I was wondering if it could be a leaking Vac. line. it has 140,000 on it.
is there some where I can get a vacuum schematic ?

but also I am almost down to 1/4 of a tank. and I just remembered last time I got low it did this but after a fill up it smoothed out.

but I would still like to know about the schematic . and any other advice.
thanks in advance.
steve