Sounds like you are describing a PCV valve (a part of the crankcase
ventillation system). In some applications they may provide a convenient
vacuum tap-off for another accessory, but probably not in your case. The
vacuum diagram label inside your engine compartment should show that very
clearly. Most likely someone just installed a 'universal' PCV valve, with an
extra port and did a poor job of capping it. Unmetered air ('vacuum leak')
sucked through there may cause unstable idling, explaining your fluctuating
voltage. Things might have gotten a lot more 'interesting' if something was
flapping around instead of just allowing a steady leak. Did you notice the
MIL (check engine light) turning on? The computer should have detected this
condition.

> The gauge instantly resumed normal operation when I unblocked the port.
> (Blocked with green electrical tape mostly sucked inside the port-clearly
> no professional install)

There is one unused port on the vacuum distribution block. The tape fix is a
hack job. Any auto parts store will have an assortment of caps that will
solve that problem correctly.

Charlie

"nashjeff" > wrote in message
lkaboutautos.com...
> Thanks for the detailed analysis, Paul. Does TAN compensate you for your
> time invested in improving their website?!
> Every car repair and maint I perform, the more often I notice once a small
> problem is found many others come into play at the same time.
> A friend of mine lent to me his multimeter and every current and voltage
> tested was optimal. Looking closer, I noticed a slight whistle where
> there should be no whistle and found a small piece of tape blocking a
> triple nipple vacuum port located on the rear of the right side valve
> cover. A larger hose continues a few inches and connects to the rear
> right sight of the throttle body. A small nipple(is this the right term?)
> protrudes forward and is definitely sucking in quite a bit of air. I can
> see no dangling hoses anywhere. Several eyes have inspected the entire
> engine compartment-nothing. Is this to some sort of electrical and/or
> vacuum sensor?
> The gauge instantly resumed normal operation when I unblocked the port.
> (Blocked with green electrical tape mostly sucked inside the port-clearly
> no professional install) The engine is a V-6 4Liter 4X4 with cruise, air,
> power. Thanks for your help
> Hunter
>

The vacuum tree makes a lot of sense. I was reading the post as something
installed in the valve cover, and he probably meant 'to the rear of'. Not
familiar with the pushrod V6, but its PCV valve is probably somewhere else,
in a much harder to access location.
One way or another, unmetered air will wreak havoc on your idle. The ten
cents spent on a real vacuum cap are a good investment.

"Charlie Bress" > wrote in message
...
> There is one unused port on the vacuum distribution block. The tape fix is
a
> hack job. Any auto parts store will have an assortment of caps that will
> solve that problem correctly.

I understand there is an extra port on the vacuum ditribution block and
that it should be plugged, but I do not understand why the electronic
fluctuations stopped entirely once it was unblocked. I allowed a few
minutes of idling so it would relearn the correct idle, as instructed in
my owner's manual. The gauge remained perfectly still. My assistant
plugged the port and the engine very nearly died and the gauge again went
haywire until it was unblocked. My check engine light has illuminated a
few times in three years, but always turns off after a few minutes or
engine restart. Help!

I would risk a guess that your IAC (Idle Air Control) valve is clogged or
otherwise inoperative, and the air supplied through that open port is
keeping your engine idling. IAC failure is very common - use Google to
search posting on this group. Pulling trouble codes out of the computer
might be very helpful to confirm (Autozone and its siblings allegedly do
this for free in most states).
Oh wait a moment, did you say it was a 92? Autozone probably won't, but all
you need to read the codes is a paper clip. This link if for the Bronco, and
the location of the test connectors might be slightly different, but
otherwise still useful:
http://www.off-road.com/ford/bigbron....html#TestPlug

Search google for 'EEC IV codes', and you will find more...

There are code readers for 92s. I have one.

Charlie

"Happy Traveler" > wrote in message
...
>I would risk a guess that your IAC (Idle Air Control) valve is clogged or
> otherwise inoperative, and the air supplied through that open port is
> keeping your engine idling. IAC failure is very common - use Google to
> search posting on this group. Pulling trouble codes out of the computer
> might be very helpful to confirm (Autozone and its siblings allegedly do
> this for free in most states).
> Oh wait a moment, did you say it was a 92? Autozone probably won't, but
> all
> you need to read the codes is a paper clip. This link if for the Bronco,
> and
> the location of the test connectors might be slightly different, but
> otherwise still useful:
> http://www.off-road.com/ford/bigbron....html#TestPlug
>
> Search google for 'EEC IV codes', and you will find more...
>
>