So I want to test the vacuum switching valve (vsv) related to the air conditioning on my 1991 4runner with the 3.0 but I'm not sure where it is located, the service manual only shows the part, not where its located. I'm pretty sure it is on top of the passenger side fender well under the engine bay, but there are 3 similar things mounted there. I think its the one with the blue connector closest to the firewall, but its right next to ones with a green and red connector.Thanks for any help guys.

 

i have an 87 and mine is located on top of the rocker arm cover. if you have
4wd you might have two like i do.

 

3vze....it's located on the pass. side fender well. Umm....run a search on Cyberman's latest threads. There's actually a pic in one of them....not the "frame up rebuild" or "rod knock" threads, but the other latest one. Sorry, I forget the title at the moment.

 

https://www.yotatech.com/forums/f116...y-part-148064/

is that the thread you were referring to? I thought that might be the a/c vsv, but the picture of it in my manual looks slightly different. In the manual the picture shows it without a round thingy above it or the black plastic adjustable screw. It also shows it as having a wire coming out of it with a connector, rather than being plugged directly into.

 

In my '94, it looks like the picture in the link you referred to above. I suspect the best way to confirm that is to trace the two hoses back to the plenum (I attached a drawing farther down in the thread referred to in the link).

But I'm curious; what are you testing for? Does you idle fail to increase when you switch on the AC? Be sure to test that you are getting vacuum out of the plenum through the port one of the hoses connects to. My plenum had a lot of gunk (I think that's the correct word) that actually blocked the port, so that the idle-up didn't work.

 

I just tested the A/C VSV, it seems to be in working order. And yes scope103, my idle does fail to increase when I turn on the A/C. Whats strange is the idle is low, its about 400-500 with the ac on and with it off, when it should be 800 with it off. I gave my truck a tune up less than a year ago and cleaned out the throttle body and adjusted the idle. I'm thinking the low idle may be the cause of the warm A/C when I'm not moving. But if the idle already came out of whack this soon does that mean there could be another problem? Is it normal to have to re adjust the idle this soon?

 

Are you sure that you're looking at the correct part in the manual and/or that the manual isn't mistaken. You must have some way to adjust the idle up and without the adjuster you can't. Also, the VSV must have an air inlet.....which is what the round thingy is....or it can't work like it should to raise the idle.

 

Okay, what do you mean the A/C VSV is in working order, given that it doesn't do the idle-up? Do you mean that the valve connects from one side to the other (by sucking through it or blowing compressed air) when the AC is on?

As a first test, pull the plenum-side hose off the plenum. That should either raise the idle (a little air is leaking in) or it should kill it (it lets in so much air that it leans out and stalls). If nothing happens, you're probably not sucking any air in through that port at all. (it should suck about 17"Hg, which you can easily feel with your finger) If you're not sucking any air, the port is probably clogged. That port is a long ways from the throttle body, so if you cleaned that throttle body and no farther it could still be clogged. You might be able to stick a 14ga wire in there, but believe me, there was a lot of crud on the other side of mine!


I dunno, but it is possible you had a functioning port AND a leaky vacuum hose, so that when you adjusted the idle during your tune up you were setting it to 800rpm WITH the idle-up on. Then when the port got clogged (or the leaky hose got reseated ....) turning off the "idle-up" it pushed the rpm way down.

First things first: pull the VSV-plenum hose while the AC is off and the truck is idling; if nothing happens that's where your problem is.

(By the way: the VSV connects air from the air box below the air filter to the plenum -- it doesn't need "ambient" air.)