'98 3.8 codes PO171/174, rough idle, shaking steering wheel

I know there are a million posts on the PO171/PO174 issue, but I am trying to troubleshoot whether or not these codes are related at all to two other problems we're having on the van: a rough idle and a wildly shaking steering wheel when driving (not just when applying brakes). It seems from searching on this site and reading Windstar's great write-ups that the codes could be from one of three things: vacuum leak, clogged fuel injectors or fuel delivery issue, or an MAF issue (what does this acronym stand for by the way? Everyone keeps mentioning it!). Now, I just need some help pinpointing which of these is actually causing these codes and I'm hoping the clues of the rough idle and shaking steering wheel will mean something to someone. Thanks for any help!

maf stands for MASS AIR FLOW

The vaccum leak issue is the most likely cause.
This likely connected to the rough idle issue.
Mass Air Flow sensor is what measures the air entering the engine.
The computer uses this to calculate how much fuel to spray in through the injectors.
A vaccum leak is air that is entering the engine from a point that does not flow through the MAF, so the computer does not know about it.....making it unable to calculate the correct fuel mix.

Clogged injectors usually show up more on 1 or 2 injectors, causing a misfire code for that cylinder.
A product called Berryman's B-12 Chemtool is a solvent based cleaner that should be tough enough to clean difficult deposits.
The injector clogging that I have seen has been inside the end cap over the end of the injector.....so it is not up inside the injector proper.....
I am told that it comes from a combination of PCV vapors and EGR dirt.
Although other things can cause misfire codes also.

Shaking steering wheel sounds like something else....warped rotor (brake disk), bad tire, are 2 things that come to mind.
Loose front end part(s) like tie rod ends can also cause this.

Having the front end checked out by a mechanic would be a good idea.

171/174 are codes that indicate that the O2 sensors are reading a lean condition on both banks. (both front and rear banks).

Since both codes are present you should think about things that are common to both banks.

Lean conditions are casued by an incorrect air/fuel mixture. The MAF sensor measures the amount of incoming air and feeds this data to the computer. The computer then determines how much fuel to add and controls this by controling the duty cycle of each injector. It is easy to see that if the MAF is reading iocorrectly or if air enters after the MAF (as in a vacuum leak) the computer will calculate the incorrect fuel mixture. Of course if the O2 sensors are reading incorrectly then it might report a condition that does not really exist. If the fuel pressure is low then less fuel will flow when the injectors are energized for their calculated duration and this will result in a lean reading.

A vacuum leak could cause rough idle. I am not sure if it could cause the steering wheel shake. Have you ruled out worn front end components?

Thanks so much for the informative posts. For now, I'm going to assume the crazy-shaking steering wheel is not related to the codes. I'll deal with that later once I tackle the potential vacuum leak/rough idle first. From searching this forum, it appears I need to remove the "cowl" in order to start trying to figure out if we have a vacuum leak and where it may be. I am a major beginner here so excuse the following: what is a "cowl", where is it located, and how do I remove it so that I can get a good look at all the potential spots for vacuum leaks? I'm assuming this is at the top of the upper intake manifold somewhere...? I am very hesitant, not having too much experience, with removing things until I have instructions for doing so via this forum.

You might want to consider the shaking steering wheel as a potential safety issue and perhaps you should look into that one a bit first.

You can always look for a vacuum leak in parallel. If it is a simple thing like a hose it can be very inexpensive to repair on your own. The cowl is the plastic/vinyl part at the bottom of the windshield. This alows you access to the back (left) side of the engine. You need to remove the wipers first.

Follow the same rules while a novice as you should as a journeyman and make sure you research first and jot notes if necessary to enable re-assembly. Get a Chilton's or Haynes as a minimum. They are under $20 and always a good reference.

There are a lot of posts on 171/174 and I believe the fix for 98s and earlier are different form the 99s and up - due to a major re-design year between 98 and 99. Make sure you are reading about your year. I believe though that the fixes are straight forward but perhaps a bit time consuming. My 99 fix took me a few hours but was not too difficult.

Eliminate the "easy" stuff first. Dirty MAFor loose vacuum loose etc. Remember this forum too. Sometimes people answer within a few minutes of your post.

I am getting ready to take a look at all of this. Thanks for the explanation of the "cowl" -- that makes sense and now I know what it's called. =) Another thing came to mind that I'd like your opinion on: when I was replacing the IMRC "cover" (don't know what it's called) on a previous repair a while back, two of the 12 bolts (I think there are 12) in the front snapped off when I was tightening them. I wonder if this is significant enough to allow a leak through the seal...? I was thinking at the time that the other 10 or so bolts were good enough to keep it closed properly, but now I'm wondering if this is the problem. What do you two think?

A definite possibility.

The "IMRC cover" is the upper intake manifold.
Broken bolts are certainly a potential cause for air to leak in.......
Don't feel bad....I broke a bolt in the lower intake manifold, which was a much bigger issue, so I know how easy it is to break a bolt.

You will need to remove the upper intake manifold again to get to the broken bolts.
If there is some of the bolt sticking up, you can grab it with the blade end of a pair of wire cutters......they seen to grip better than pliers.

If there is not some of the bolt sticking up.....you will need to use other means.....maybe what is called an "Easy out" which is a tool specifically designed to remove broken bits of bolts.
In this case, I would pay a vist to your local hardware store for advice on the correct tool.....and how to use it.
I would try something like a Ace or True Value hardware store.....and not one of the "big box" places.

The upper intake manifold gaskets are re-usable, make sure that they are all in place in the grooves on the bottom of the upper intake manifold.
Also make sure that the top of the lower intake manifold, where the gaskets are going to be touching, is clean......so that you will get a good seal.

Of course, be careful to avoid over tightening the upper intake manifold bolts.
They give you the order to tighten them and the torque specifications on the AutoZone website, under vehicle specific repair guides.
Remember, INCH pounds, not FT pounds.......a very common mistake.

Thank you so much for all of the excellent advice. Due to weather and work, I was only able to get back to work on the van this weekend. I managed to get the broken bolts out with success. I tried getting the replacement bolts from the local Ford dealership and they were closed and only open again today -- joy, joy. I am heading over there soon after work to get the new bolts to hopefully finish the job. I've come across three more questions for you in the meantime:

1. Once I have taken off the upper intake manifold, dust and dirt has gotten between the seal so how do I clean that (what kind of cleaner?)?
2. Do I need to add anything to reseal it (like grease) before I close it up again?
3. How do I know if the gasket needs be replaced?

I did check for vacuum leaks while I had the cowl off. I did a good visual inspection and listened for hissing/whistling with a stethoscope I had. I didn't really find anything with my untrained eye/ear at this point. Many of the vacuums had some minor surface cracking starting to show, but no cracks that I could find that had gone through enough to allow air in.