Aux. Air Regulator and Air Valve?

RazorRacer · 06-08-2002, 06:05 PM

What is the difference between the Aux. Air Regulator and the Air Valve? Do they somehow work together? Please explain.

1bar · 06-08-2002, 08:18 PM

Boy, I get confused about these beasties too. I'm by no means an expert, so I'll tell you what I have "figured out" - it's up to you to figure out if I'm full of beans or not. On my '77 930 I have:

Auxiliary Air Valve - this is a 1in square by 5in long gizmo with a 3in square 1/2in thick flange at one end. Two large braided hoses come in and out of this flange, and a 2-wire electrical plug powers it up. There is a round valve inside that allows air to bypass the throttle body butterfly when the car is cold. This unit is mounted such that it is thermally isolated from the engine (on rubber feet). There is a thermal element inside that keeps the air bypass open for a predetermined time after you start the car, and then it rotates the valve and closes off the airflow (it's all up to your foot now).

The OTHER Auxiliary Air Bypass Valve - this is a ~4in diameter diaphragm in a ~1in thick "can". It has two larger hoses on one side that, when the diaphragm is open, allows air to bypass the throttle body butterfly. On the other side is a small vacuum control line. This line runs up to an electrical control element the size of a matchbook, which is mounted on the fuel rail to measure the intake rail temperature. This thing is electrically controlled (has another 2-wire electrical plug), and keeps the valve open by supplying vacuum during cold starts and at cold air temps. It closes when the car is on long enough if the fuel rail is up to temp.

Then, there's the Deceleration Control Valve - it looks just like the last one, but it's vacuum control feeds directly from the intake. When you suddenly let off the gas after heavy throttle, this diaphragm opens and lets air past the throttle body butterfly to slow down the engine deceleration, supposedly reducing emissions. This thing just never worked in my car, so I plugged the vacuum line up with a ball bearing and have been much happier ever since.

You now know just about everything I think I know. Hope it helps!

RazorRacer · 06-08-2002, 11:48 PM

So the air valve is based on a timer and the aux. air regulator is based on temperature. Thanks.

Pelican Parts says "Rough running when the car is hot may indicate a defective unit* that has stuck open."

*Aux. air regulator

Can anyone give more description than "rough running"?

1bar · 06-09-2002, 09:08 AM

I just looked up in the PET to compare my names with what's listed there. The first valve I described is called the Auxiliary Air Regulator in the PET, p/n 930 606 102 00. This is the long square box with the flange on the end.

When this thing was stuck open on my car, I had a high idle that could not be adjusted down below 1100RPM with the idle screw. When you backed off the gas, the RPMs would die to near zero, and recover in ~1sec. I replaced the bugger and the idle adjustment now works, and the engine doesn't try to die every time you back off the gas. It didn't run rough at all - except for that attempt to die whenever you pulled up to a stop sign.

The thing that I called a Deceleration Control Valve is listed as a "Vacuum Limiter" in the PET, p/n 930 110 173 00. This is the gadget that attempts to retard the engine RPM change as it returns to idle after you let off the gas from heavy throttle.

I can't find the OTHER valve on my model car in the PET - but then it frequently takes me a hour to find where they stick some of these parts in their pictures.

In my experience, really rough running has been due to a vacuum leak (something I forgot to put back on

).

Good luck.

RazorRacer · 06-09-2002, 12:27 PM

1bar, if your Auxiliary Air Regulator was stuck open, did the car behave fine when cold and then begin to act up when hot? That would make sense.

1bar · 06-09-2002, 12:31 PM

No. It was relatively hard to start, but performance didn't change appreciably when cold vs. hot. Possibly the speed dip might have been worse hot, but it wasn't a big enough difference to make a real change.

wckrause · wckrause's Garage

Quote:

This line runs up to an electrical control element the size of a matchbook, which is mounted on the fuel rail to measure the intake rail temperature. This thing is electrically controlled (has another 2-wire electrical plug), and keeps the valve open by supplying vacuum during cold starts and at cold air temps. It closes when the car is on long enough if the fuel rail is up to temp.

If you're attempting to describe the function of the thermovalve, then you're a bit off base. The thermovalve switches vacuum only to the WUR (closed for cold start, open when warm). Engine vacuum is always present on the decel valve. It's also not mounted on any fuel rail. It's mounted to the bottom of the bracket that holds the aux blower. (There is no such thing as a fuel rail on an SC).

This diagram shows the correct vacuum connections for 78-79 SC's

http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-2.JPG

1bar · 06-09-2002, 09:22 PM

Hi, Bill. I've never had an SC, and from your diagram there are quite a few differences between my car and yours. I didn't realize just how different.

I wasn't talking about the warm up regulator - I've got another valve that looks just like the deceleration control valve, but is contolled by an electrically switched vacuum line. The deceleration control valve has vacuum always in place - it's mounted to the rear of my motor, while the other unit is mounted to the front. My auxiliary air regulator (your #36) is mounted above cylinder 5 - which is also quite a bit different than your diagram. I do not have an object that looks like your #7. Both of the valves I'm describing look like your #39, except that they have a vacuum line coming out the other side.

Razor, you should probably listen to an SC owner - looks like CIS is not always CIS! I guess with all the smog changes over those years, one shouldn't be surprised.