Testing ACV?
 

How do I go about testing the ACV? S5 T2. Hailers, you seem to be an expert on the emissions goodies ;)

I'd go to the FUEL section of the online manual at http://www.iluvmyrx7.com and there is a page or two on that.

Why is it suspect?

Intermittent buzzing sound coming from it when it's cold, and I think I have an internal air leak, because there are no vacuum leaks. Someone else suggested that the diaphragm might be leaking air...

Simply put, car runs rich as shit. TPS set. BAC tested. Issues are mostly at idle (1000-2000RPM misfire). Issue goes away with the A/C turned on (bac kicking in).

Do a few simple things. Buy for fifty cents a piece of vacuum hose at PepBoys. About two feet.

On the bottom of the acv is a mushroom device that has a nipple. Put your new hose on that nipple. Now suck on it and see if it will hold a vacuum. If it will, good. If not the diaphram is busted. Now if it holds a vacuum, pull the large hose off the bottom of the acv. Put your finger in the hole til you feel the spring inside. Now BLOW into the same nipple on the mushroom. You should be able to feel the spring move. Thats good. So that part of the acv is probably good.

Now at the top of the acv is a nipple that sticks straight up. Put your new hose on that one and suck. It should hold a vacuum. If not, the diaphram is toast and needs repair or replacement of the acv. If it holds vacuum, thats good and fine. That diaphram is the one that rots first (imho).

There is another diaphram in the acv that can go bad and WILL effect your idle real bad. Its the only part of the acv that puts fresh unmetered air into the INTAKE. Its the anti afterburn valve and diaphram. On deceleration the intake manifold will suck this diaphram/valve open and let fresh air into the intake to reduce emissions and prevent backfire. IF this diaphram/valve is busted, at idle it will let unmetered air into the intake and, well, fuck up your idle. To prove this item in the acv is bad, do this: buy some STARTER FLUID. Take the hose off the air filter box that feeds the air pump. Now while the car is trying to idle, spray the starter fluid into the airpumps air intake hose for a second or less. IF the idle picks up.....that diaphram/valve is deteriorated/busted/ crummy/no good.

The one half ass good acv for a turbo that I own has a slight problem in this very area. Not real bad, but the thing is leaking a touch. Enough to change the idle if I take the acv off and block off the acv.

One other thing might be causing the noise. Maybe the check valve that is located b/t the acv and the intake is busted. That won't effect idle, but could be making a noise if busted. YOu have to take the acv off to examine it. Its about the size of a silver dollar and is recessed in the intake manifold about 1/16 inch. Black in color.

I'd do the starter fluid thing , then the vac hose things.

Note: only one of the nipples gets vacuum. The one sticking straight up in the air. The bottom one GETS air pressure from the relief solenoid. The one in the middle is a passage for airpump air to travel to the other side of the engine to the relief solenoid to feed the bottom nipple when the time comes. The nipple at the top that sticks straight out at you, is just a passage for boost/vacuum pressure for the boost sensor. Enough.

I just thought. Is it possible that you have the three vac/pressure lines to your turbo's acv crossed up????? On a N/T they are all vacuum, but on a turbo two of the three are pressure lines. Only the one on top that sticks straight up is vacuum.

Fack i donno what's going on with this damn car. Alright i popped the air filter off... idled the car without the filter ... issue got much better, but still very much there.

But with the ac on (and i guess the bac providing more air), the issue is pretty much nonexistant.

DRIVING ME NUTS!

Any ideas?

So...what happen when you take the intake hose for the airpump off, and then spray some starter fluid in the hose? P.S leave the air filter in place.

Turning the a/c on will cause the ECU to add a touch more fuel. IF you watched the duration of the fuel injectors you would see that they stay open a touch longer. Say 3.0 ms at idle and then maybe something like 3.3 ms with the a/c on.

I'll try that

I thought turning the ac on provides more air and leans out the mixture because the BAC is now active?

The BAC is active most of the time. Mostly at idle. If you add an additional load to the engine, the bac's duration is longer feeding more air. IF you monitored the primary fuel injectors you'd see their duration go up also. See http://www.teamfc3s.org/info/articles/idle.html for a good description of the working of the bac.

If you have a buzzing from the acv, just do one thing at a time as described in the earlier post. First take the three hose off and see if they are routed right. Vacuum only to the one at the top that sticks straight up. Then check that the other two go to the blue solenoid. Both pressure at one time or the other.

Hey, thanks, Hailers! I checked my ACV as per your stef - used a vac gauge though.. it didn't hold a vacuum.
Now my question is: do I need to replace the whole thing, or is the diaphragm replaceable?
(a noobie with a 91-vert).
thanks for any help!

K tried some of them... here's what i found:

Hose sticking straight up only gets vacuum upon deceleration, it seems. I didnt test the diaphragm yet. I want to pick up a vacuum pump first.

Bottom hose is UNREACHABLE. Or if i do reach it, i will never get it back on. FACKING ABS!!!!

I replaced the vacuum hoses that i could see... and they were hardened to a rock-like texture.

Tried the fluid thing except i used WD40 (anything flammable will usually do if used in small amounts) and it didnt affect the idle at all. I should have, however, sprayed it when the car was misfiring/backfiring.