How do you replace the air filter on a 2000 Ford Focus when the bottom of the bolts just spin or are frozen?

I'm posting and answering this question because it took *forever* to find an online source with the repair to this common problem!

At the base of the 2000 Ford Focus air filter housing, there are four circular "nuts" which the corner bolts thread through to tighten down the top. It seems these can come loose from the plastic "sleeve" which held them secure from the factory -- when that happens, they just spin when you try to remove the bolts and change the air filter. There is very little room around the box to get at the bottom and hold onto them as they spin, and they aren't true nuts with a hex edge so it's very hard to get a grip on them. My first thought was to remove the battery which would allow more access to the front two, but the fuse box is up against the back two so that wouldn't do much good.

Here's the fix... Remove the hose clamp at the top and wiggle the air hose off. There is also a small sensor that just clips onto the top of the housing, and a small hose on the lower left side (it leads into a small compartment with a breather element). When you clear those three things, pull straight up on the air filter housing. It should pull right up and out; don't wiggle it too much back and forth because there are three plastic pieces which extend from the bottom and are loosley seated into rubber gaskets.

Once you pull it out you can get a socket onto the top of the bolt, and some needle-nose pliers or small channel locks onto the rounded nut. I used a good amount of WD40, and found that going tighten-loosen-tighten-loosen a few times was the trick to freeing the bolts up for removal.

Good luck!

Note: if the round nut still spins with the needle nose plier, you will need Vise grips to lock down the nut. In order to get the mouth of the Vise grips around the nut, use the needle nose plier which failed earlier to break the gussets that are molded into the box which flank both sides of the nut. Make sure the teeth of the vise grip bite into the nut (parallel to nut, perpendicular to bolt).