TheSamba.com :: View topic - Rough Idle-- Auxiliary Air Regulator Valve?

Fri Dec 16, 2022 10:46 am

Hi All, I am helping a friend with his 1978 Westfalia. It started to idle very rough on cold starts to the point it shuts off. We have to leave it running and rev a little for 20 minutes until it warms up and runs a bit better.

The symptoms started all the sudden as soon as we received colder days. Someone suggested it could be the Auxiliary Air Regulator Valve? I have been looking for it but I can't find the darn thing. Could someone point to me in the right direction to the location of it?

Here is a picture

EDIT: Moved to the right group! Sorry!

Fri Dec 16, 2022 10:59 am

While there are many here who know the air-cooled well - the Bay Window Bus forum is for the year you listed -see https://www.thesamba.com/vw/forum/viewforum.php?f=5

Fri Dec 16, 2022 11:03 am

It feeds air directly into the intake plenum in the middle top. The thing with the 4 outlets to the cylinders has a largish device with wires and a hose connected to the air intake. There is also another fuel injector "cold start valve" and also a temperature sensor in the cylinder head.

I'm not experienced enough to advise and sound like I know what I'm talking about, but I'd suspect the temp sensor. There are ways to troubleshoot all the cold start features. I'm sure someone will be along presently.

But this is the Vanagon forum (buses are on aisle 3).

Fri Dec 16, 2022 11:25 am

Look for a vacuum leak in the hoses to, and out of, the Aux Air Valve. Check all the other vacuum hoses, the intake runner hoses, for leaks as well.
If you're going lean once you get it started due to vacuum leaks, the extra air bypassed by the Aux Air Valve can't give you the normal, higher cold idle engine speed since you're losing air flow control.
A gentle spray of Carb Cleaner or Brake Cleaner around all the above ^^^^ listed hoses can help show where a leak or leaks, might be.

Fri Dec 16, 2022 12:19 pm

Thanks everyone! I made the mistake of posting in the wrong aisle. If a Mod can move it?

I'll take the advices of the vacuum leaks.. yet I still don't know where the Aux Air Valve is... :(

Fri Dec 16, 2022 12:43 pm

Cold start problem, Things to check
a, Cylinder head temp sensor resistance should be way more than 1k cold (upto 15K extreme cold)and less than 300 ohms hot
b fuel pressure
c. cold start injector but not for your problem.

Vacuum leaks effect summer and winter so not your case unless cold start valve case is split .

Fri Dec 16, 2022 2:15 pm

Where would the temp sensor be?

Fri Dec 16, 2022 2:34 pm

it's on the driver's side towards the front of the vehicle.

Here's a thread with pictures:

https://www.thesamba.com/vw/forum/viewtopic.php?t=361999

Fri Dec 16, 2022 2:37 pm

Another thread, half way down there's a shot of where the valve would be , next to the intake manifold. In that picture, the valve is off the engine, but you can easily see the little stub nipple coming at an angle off the intake manifold. A short elbow hose connects the vavle to that nipple, then you have a hose out of the Aux Air Valve over to the Intake Manifold. Look for appox 1/2" diameter hoses at your intake boot, and work back toward the engine center as noted.
You should find the aux air valve then, right next to the intake manifold as the picture shows the mounting plate the Valve gets screwed to.
https://www.thesamba.com/vw/forum/viewtopic.php?t=86388&highlight=aux+air+valve

Another thread, very clean engine with Aux Valve bolted in, and hose attached to the Intake Manifold for you... just scroll down a few pictures to see it.

https://www.thesamba.com/vw/forum/viewtopic.php?t=708208&highlight=aux+air+valv

Fri Dec 16, 2022 10:22 pm

gup_08 wrote: Thanks everyone! I made the mistake of posting in the wrong aisle. If a Mod can move it?

No problem, moved.

Sat Dec 17, 2022 12:07 am

start with a look for a vacuum leak.

S-Boot cracked
hose off
Broken hose
bad brake booster
worn out injector seals

Best test is to use a smoke generator. If you don't have one get a clean METAL paint can, poke a hole in it and stick a hose in. Put another hose in it to put in GENTLE compressed air. But a cotton ball with some mineral oil on it or an old cigar or like that you toss in the can and flood the AFM inlet with the air cleaner 1/2 off. stuff some clean rags to keep the smoke where you want it then look for where you see smoke. Any leaks will be obvious.

Chasing any other low failure parts is likely to make life more complicated until any vacuum leaks are found. On the FI engine even the oil cap being off can make it run like that. Worn out injector seals can cause so don't ignore them.

If you want to test FI parts like the aux air valve start here. https://www.thesamba.com/vw/archives/manuals/afc_f...Manual.pdf

Sat Dec 17, 2022 4:54 am

Check the S-boot for cracks in the pleats. Rubber items like hoses and boots harden in the cold and thus cracks tend to open up. These items also tend to be in worse shape on their bottom sides where the damage is less easily seen.

When one buys one of these old rigs, it often pays to just go through a replace all the old hoses and boots and get rid of all the problems at once. As for the AAR, it does the same as opening the throttle a little bit, so if opening the throttle a tad doesn't cause the idle to clear up then the AAR is likely not the cause or at least the whole cause of your rough running.

Have you added FI cleaner to the tank. Old stinky ethanol laced fuel doesn't age well and will gum up injectors quite readily. MMO can help keep injectors from sticking.