Hi everyone, while checking coolant the other day I noticed that this vacuum line appears to have been deliberately unplugged and tucked away over the radiator. I hesitate to just hook it back up in case it was removed for a reason, can anyone identify it?

 

I believe that's unmetered air (not vacuum) for the PAIR valve. http://web.archive.org/web/201311071...78pulsedse.pdf

The other possibility (my drawings aren't specific enough) is that it is metered air for the A/C and PS idle-ups, but I'm pretty sure it's for the PAIR.

Why? The PAIR has four screws, and with vehicles of your vintage they might get loose. This produces a buzzing noise. Tightening those screws (or replacing a few if they fell out) will stop the noise. Or, you can just go caveman style and pull the hose.

 

You know, its interesting you mention the A/C, as the truck runs great except when the A/C is running at idle. I wonder if this might be the cause. Guess I will have to hook it back up and see if it explodes.

 

If it's metered air (for the idle-ups), the fact that it's disconnected means a big "vacuum leak." For whatever reason it was disconnected in the first place, someone might have adjusted something to overcome the leak. Meaning: don't be too surprised if hooking up that line causes you to run "rich." At least until you find the underlying reason for it in the first place.

 

That's a nice and shiny alternator. Did you install it or someone else?

 

Alternator was installed by a previous owner, not sure what brand, but it does have a refurb badge on it.

 

I only ask because you need those hoses out of the way when you remove or install the alternator. Who ever did it probably forgot to re-attach it. Did it solve your AC problem?

 

Weather has been so nice here I have been riding the bike instead of taking the 4Runner. Hooked the vacuum line back up today, it does indeed seem to have fixed the weird idle with A/C on. Also looks like it may have fixed an issue where the truck has a super rough idle after being run, sitting for a bit, and then starting again. Will keep an eye on it.