AAR - How much should it open?

ZV8888 · 07-26-2008, 01:50 PM

After leaving the car to cool down for 3 hours, I took the pipe off the aux air regulator valve and took a look inside with a mirror. It only had an opening about 1/5 of the area. I was expecting it to be fully open. I am in Ireland where the ambient temp rarely goes above 15C in the Summer (approx 50F). It looked a bit like this at 12:57 (Sun Pic 2):

So I took it off and cleaned it out. The opening never enlarged. and I found there was a lot of engine oil to drain out of it. I could open it wider with a small screwdriver but it always sprung back to the Sun pic 2.

When the engine is warm, it is fully closed.

Is this expected behaviour or is the damn thing faulty?

I've been trying to track down a problem where when you start up and it's cold, the revs don't go above 800 and accelerating makes no difference. After a minute or two, it springs to life, but runs a bit lean. After another minute or two things richen up and all is pretty good.

Warm start is fine.

The Idle mixture needs to be adjusted on a regular basis ..... a few days after you think things are just right, it goes dodgy again.

Could this problem be down to that silly valve not opening fully when cold?

Thanks

SP2 · 07-26-2008, 01:53 PM

That cold start description is my problem too with the SC. Subscribing.

Bobboloo · Bobboloo's Garage

3 hours may not be long enough for a complete cooldown. If however the motor has cooled completely and it's 50 deg. F then that opening is to small.

The AAR is basically a bi-metal strip with a valve, spring and a coil. I believe what happens over time is that the spring warps the bi-metal strip. You can drill out the rivets to open the case and then bend the strip away from the spring tension. After a desired amount is achieved then just close the case with some small bolts and nuts. Piece of cake.

Once I recall seeing some specs for these things regarding the proper calibration but I can't find that info.

Test on your motor to see if you are getting the desired idle RPM for the ambient temp. If it's too high or to low then bend the strip accordingly.

gsmith660 · 07-26-2008, 03:35 PM

The way I have always been told to test the AAR is to put it in the freezer and it should fully open then use wires and apply 12 volts to it and it should fully close within 2 to 3 mins. Hope this helps. I have 2 and tested both that way and both worked as advertised. I will look at my spare that is not in the car and see how far it is open it is almost 90 here right now.

gsmith660 · 07-26-2008, 04:09 PM

At 90 F out mine is open to approx. the 13:09 position on your photo above maybe a little more so I would venture yours needs replacement or I have seen threads that go into repairing and cleaning these. I would try the freezer test and a good cleaning.

tdatk · 07-26-2008, 07:25 PM

I have the same issue. Iv'e been compensating the idle issues by running rich. I have found that my injector sleeves leak by on 3 injectors. check is easy, when warm, spray carb cleaner on the injector and see if your idle changes. If so, your injectors are letting air past them. My cis is 27 y/o and way over due to get some attention.I believe most of my idle issues are in the pintles.

SP2 · 07-26-2008, 08:31 PM

My cis does this and I re-did all my injectors with new seals last summer and had john walker pressure check all six injectors FWIW.

ZV8888 · 07-27-2008, 12:40 AM

Thanks guys for you help. This morning it is a nice warm summer day here in Ireland. So it's about 19C or 68F. My thingy was open to about 13:12and started pretty well .... better than most days. I will try the freezer test in the next few days when i get a chance. Yesterday I also took the famous WUR apart and cleaned a small amount of crud out of the gauze maybe that helped too. After starting it is taking the bit of throttle I give it, so it's much better. I can use the hand throttle to keep it at 1500 for a few minutes till it gets warm. Then things are good.

gsmith660 · 07-27-2008, 04:50 AM

hope things improve for you, good luck.

Jim Williams · 07-27-2008, 07:48 AM

VZ8888 -

Bosch made a bunch of these AARs. Maybe 4 or so for the normally aspirated US 911 CIS cars alone. They all have different characteristics. Different times to warm up and different opening sizes when "cold", depending on how you define "cold". As far as I know, there are no published numbers for either the time to warm up, or the size of the opening when cold. Also the "shutters" inside the AARs have different shapes as to the edge of the shutter that closes off the opening. Some are circular, and some have a rectangular slot cut in them. So your opening size may be fine for the type of AAR you have.

Depending on who answers your question, and what type of AAR their experience is with, you will get different responses on what is the right number. Also throw into the mix the age and condition of the particular AAR on that individual's car. Several AARs that I have seen have "cold" openings such as you describe.