Sounds like you have over 2000 in parts ni this thing, is it worth much
more than this?

I agree.  It was the fact he never communicated to me that he was just
"guessing", and he also never experienced the problem himself but never
told me that either.  I'd been assuming that he'd test it, see that
something was wrong, fix something, test again and it would be okay.
But no, he was replacing things blindly.

I still haven't had chance to contact the dealership about it, but there
are a couple more bits of information that may be important.

I had the fuel filter replaced, and the fuel pouring out of the old
filter was black!  I'm guessing it hadn't been replaced for a LONG time.
 New filter made no difference to the problem though.

I tested the voltage to the fuel pump while the problem was happening,
and it remains constant, so no electrical problem form that side.

I found that I can get it to happen fairly regularly on a particular
hill.  If I'm on this freeway hill doing a steady 70mph, I will get 2
rapid stumbles (within 1 second) almost exactly every 4 seconds.

Dunno if any of that info sheds light on anything else, but the regular
stumble might point to the CKP sensor.  I don't know for sure, but it
might be worth trying having come this far with it.

 Intermittant drivability concerns are probably THE toughest problems to properly
diagnose on any vehicle. Even for Techs specifically trained in one manufacturers
products. The particulars of the engine management systems, although similar in
concept, vary widely between car makers. It's an impossible task for a Tech at an
independent shop to be an "expert" in diagnosis of all the different systems. Most
driveability symptoms are easily diagnosed, but there are always a few that will lead
to head scratching even by a competent Dealership Tech.
 I wouldn't hold not being able to find the problem against the fellow that worked on
your car. What I would hold against him is the fact that he didn't stand behind the
"repair" and kept charging you for parts that you didn't need. That's just bad
practice. He should have informed you that the problem was beyond his scope and
offered an adjustment to the original repair price.
 Good luck, and let us know how it turns out.

No, he's not a Ford Dealer, but he *was* someone I trusted to be able to
understand how a car works and provide a reasonably accurate diagnosis.
 There's an element of trust needed in these situations since I'd
expect a mechanic to be an "expert" in matching symptoms to problems.
This however, was not the case.

As for being charged for repairs that didn't change anything.  He'd
inform me that "the MAF tested bad and needs replacing" and so on, so
I'd pay for a new one then collect the van.  Because the problem is
intermittent, it wouldn't show up for a day or so before I'd call in and
take it back.  Of course, he never kept any of the original parts, so I
got kind of screwed over.  That's why he's not touching it again.

I value your advice, so I'm going to give my local ford dealer a call
today, and see if I can get a diagnosis estimate.  If it's just a hour's
labor I'll go ahead and do it to see what I'm up against.

Yes, but was this "shop" a Ford Dealer? If so, I stand corrected. If not, well....
 Until 2001, I was a Ford Master Tech. If I had your vehicle in front of me I could
very likely find the problem fairly quickly. To this day, I tend to choke on GM
vehicles, even with the factory documentation. Given that, is it entirely fair to
expect a "General Mechanic" at an Independent shop to completely understand your Ford
vehicle, especially with an intermittant concern such as yours?
 If you are being charged for repairs that don't solve the problem, it's not the
shops fault. Why are you paying the bill?

It's already cost me over $1500 at the shop, and they were just doing
the same as me, replacing things blindly and costing me money.  At least
when I do it the parts are a lot cheaper and the labor is "free".

But yes, if I could find a mechanic that could diagnose the problem with
100% reliability before it started costing me money, then I'd be there
like a shot.

Unfortunately it seems that most mechanics go the easy route because
it's not their money that they're burning through, and as a bonus they
get to charge labor for fitting unnecessary parts.

I'd like to chime in here. You've tossed a couple of hundred dollars at this problem
by replacing parts that it didn't need and failed to fix the problem. Did you ever
think that maybe it needs a trip to the dealer to fix it once and for all? What you've
spent already would have likely covered the cost of the repair originally.

Here are a couple more videos, just idling and revving.  Nothing really
shows up here, apart from on the revving one, but I think I'm just
hitting the rev limiter on that one (hard to tell with no tacho).

Idling
http://s15.photobucket.com/albums/a388/InstantArcade/windstar/?action=view&curre
nt=IMAG0005.flv

Revving
http://s15.photobucket.com/albums/a388/InstantArcade/windstar/?action=view&curre
nt=ff2867f5.flv

Since I can't seem to get it to occur in N or P I'm leaning back toward
it being a transmission problem again.  Is there ANY way of finding out
for sure that it's the transmission?  I still get the same symptoms with
overdrive OFF, and also if I tell the transmission to maually stay in
1st or 2nd (with the shifter) it still does it.  Does that mean it might
be the transmission control solenoid (AXODE-AX4S; 4 spd; 17 bolt pan;
on/off lock-up solenoid) ??

I'll try to get some better video/audio footage of the problem.  The
vehicle does shake/buck pretty hard when it's doing it.

Still broken :(

I also put on a new DPFE last night.  That was a horrible job (I just
hope I don't have to change the EGR, it seems like you'd have to pull
the motor to do that).  Who's clever idea was it to put the DPFE on the
rear of the motor facing the firewall?  I mean, AT LEAST use attaching
bolts that face the front of the engine bay where you can actually get
to them.  Oh well, there's another tool that's forever lost somewhere in
the engine bay :(  Now I'm all cut up and burned :(

Anyway, the new DPFE made no discernible difference either.

I have a replacement fuel filter to put on this weekend (that's one huge
mutha), but I doubt it will make any difference.

Is it worth trying a new fuel pressure regulator?  Would a faulty one
starve fuel so rapidly that the vehicle splutters and bucks?  Or am I
barking up the wrong tree?

There's also the possibility of changing out the CKP and the VSS
(although I have no idea where the VSS is on the 3.0 motor).  I'd rather
not spend more than I need to so if any knows if either of those
wouldn't help then let me know.  I'd expect a faulty CKP to throw a code
at least.

It has new plugs, new wires and a brand new MAF, much to the distress of
my wallet. No replacement fuel filter yet, but I wouldn't expect such
harsh symptoms from a dirty filter.

I just changed out the coil pack myself about an hour ago (for $64), and
drove back to work.  Okay so far, but then it can run fine for a while.

If it's still good after a week, I'll concede that the coil pack was the
culprit.  I'm not holding out much hope though, so I still preemptively
have replacement VSS and CPK sensors on my "to buy" list.

have you done the obvious like plugs, wires, and fuel filter? And clean
the MAF...? At your mileage it needs it anyway. Is there a certain way
to drive it to make it do it for a longer period of time to set a code?
If you can get it to do it long enough you will get a missfire code that
will point you to the right cylinder at least.

I have a 98 Windstar 3.0 with 128k miles on it, and over the past few
months it has had a problem with hesitation and bucking.  The problem is
intermittent.

My mechanic has diagnosed a few things so far and a lot of money has
been spent on 'repairs' but nothing he suggests fixes the problem.  I've
now taken it back from my mechanic and his "shotgunning" repair
technique in order to try and diagnose the problem myself.

So far I've replaced the Throttle Position Sensor and the Camshaft
Position Sensor, and while that seemed to fix it for a day or two, the
problem came back.  (It's intermittent nature means it can run fine for
days).

There seems to be no rhyme or reason to the hesitation, it can happen
when you're pulling away gently, or when you're cruising at highway
speeds, or during a shift, pretty much any time.  Turning overdrive off,
or keeping the transmission in 1st or 2nd makes no difference.  Also you
can drive it really hard sometimes without the problem manifesting at
all.  Often I'll drive it hard 10 miles to work and it's fine, then it
will act up on the way home with about 3 miles to go.

As good as I can tell it feels like the engine is cutting power to the
injectors or plugs all at the same time.  And the loss of power can last
from a fraction of a second to a whole second before it recovers.
Sometimes you just feel a bit of spluttering as though only a single
injector or plug isn't firing.  I thought it might be a transmission
problem, but I'd imagine that the revs would climb while the
transmission slips, and that's not happening.

I've also had poor idling on occasion, but it's very uncommon, so may
not be related.

Any ideas what to try next?