And all the kings horses...

Ok...The story thus far followed by the questions to date.

doing an upper and lower manifold gasket on a '98 windstar 3.8L. I got my new manifold gaskets and the new IMRC and I now have everything cleaned and ready to go back together (I'm stopping for the night becuase I'm exhuasted). I took inventory of what I have and noticed that there may be a few things missing...

There is a coolant tube running through the intake manifold, do I need to replace the O-ring on that? This enters the intake on the passenger side of the manifold and goes all the way through with a tappered end.

A better question would be do I need to replace all the O-rings on the coolant hoses that go to the intake and can I get those from a normal parts store? The O-rings look to be in decent condition, but I do not want to have to repeat this procedure if I can avoid it.

The thermostat houseing gasket, does that have to be replaced? Again, it looks to be in good shape.

I've already replaced all the O-rings on the fuel injectors, but is there anything else I should replace while I've got the intake off? I'm very, very, very new to these types of repairs on fuel injected/sensor driven engines so I'm not sure what "needs" to be replaced and what's just a good idea. Any help here would be much appreciated.

Trons
"In the land of the blind, the one eyed man is king."

I did this job recently following a P0304 code. I cleaned everything thoroughly but didn't replace anything that didn't come in the gasket set such as the 'o' rings you refer to. Of course I inspected them closely but anything that looked ok I left in place. Now that you've been in there once it's not such a big deal. I intend running the windstar into the ground so I half expect to have to remove the manifolds to clear the egr ports at some time in the future.
If you have the thermostat housing off then you'd have to replace the gasket but other than that no and I certainly didn't bother given that I knew the thermostat was fine and just left well enough alone.
I think an oil change with filter is unavoidable at this time as I found it impossible to prevent a few drips of coolant getting in.
I also had to replace the DPFE sensor - good advice if you've still got the aluminium bodied version (the newer ones are black plastic) and have had coolant leaking into one or more cylinders.
My van is running beautifully (for now at least) with no loss of coolant since the manifold job and no cel.
I for one certainly appreciate the advice I got from members of this forum and I'm happy to pass on anything I can tell you from my experience.

Ok, I got it back together and started it, it seems fine...except...when it's reved up around 4K rpms it starts "chugging". I'm not getting a CEL and if you let the rpms come back down, it's fine. Drivablity: doesn't seem to have quite the power that it had before but not so much that it's a rough runner. I've driven up the road and my wife drove it to the store about 4 miles away and this seems to be about the only problem so far...I just don't know where to start looking.

My plan is to start taking it back apart and see if I made a stupid mistake, but I'm hoping somebody might be able to point me in the right direction.

I Replaced the lower intake manifold gasket, the air plenium gaskets and the front IMRC.

Trons
"If it ain't broke, fix it anyway."

above 4K rpms?... But fine up to that?
The first thing that comes to mind would be fuel delivery......
As I like cheap fixes, first thing I would think of would be the fuel filter.

I know that you had the fuel pressure regulator off to do the repair....but it is pretty easy to install....(just replaced mine today).....but less likely a problem.....double check the vaccum connection to it.

Make sure that you change the oil and filter...

I would take it for a nice drive (over 50 miles) and see how it does....
See if it throws any codes, etc. before taking anything apart....unless you find something leaking..

I would NOT recommend reving up to 4K rpms in the driveway...at least not very much. After your 50 mile drive, with no problems.....You might see how it does with a few full throttle accelerations....

Agree with wiswind but first I'd check and re-check all of the connections particularly the vacuum lines.

You say it starts chugging at about 4K rpm,, Is this in park or neutral with no load,?, if so it could just be the pcm protecting your engine with the built in rev limiter.. If so it's quite normal. You may have not noticed this before since it's not a normal driving habit to rev the engine.