Bad Auxillary Air Valve??

code7rpd · 08-28-2006, 08:50 AM

I think my Aux Air Valve might be bad. The rpm's drop rapidly and when coming to a stop the car will die unless I blip the throttle prior to taking off. Any ideas on how to test the valve? I checked to see if it was holding vacuum and it does.

jason2guy · 08-28-2006, 08:57 AM

thats not the valve most likely. could be mixture, timing.
what yr car etc......

ruf-porsche · ruf-porsche's Garage

Once the engine is running the AAR should be fully closed. The AAR is opened when the engine is cold to allow additional air beyond the throttle plate. You should check that it is fully closed and not leaking air when the engine is warmed.

code7rpd · 08-28-2006, 09:18 AM

I think I may have the names backwards - the valve I am thinking about is not the AAR which has the electrical connection but the valve behind it - it looks like a large dashpot. The car is a 1981 SC with a 3.2 shortstroke. The mixture is set at 2.0 CO with the timing at 7 degrees and the cold fuel pressure is set at 1.8 bar. I just had the mixture set because the cold pressure was too high causing a lean mixture when cold.

arcsine · 08-28-2006, 10:02 AM

Deceleration valve?

PhatA55 · PhatA55's Garage

Is the highlighted part the one you're talking about? If so, read about the deceleration valve here: http://members.rennlist.com/jimwms/CIS/CIShome.html
I'm dealing with this now.

arcsine · 08-28-2006, 10:51 AM

The item highlighted above is the aux air valve and not the decel valve. The decel valve in this diagram is #12 (on the far left/middle). The design of the decel valve changed over the years and came to look almost identical to the aux air valve but the decel valve sports a small fitting on the opposite side from the large fittings.

On the pic below (from left to right) are the older (used until '79) decel valve, followed by the aux air regulator, the aux air valve and last the newer ('81-'83) decel valve.

The decel valve is designed to moderate the slowing down of the engine when coming off throttle. Many people have sucessufully disconnected them with no ill effects except maybe needing to manually moderate the throttle when stopping.

arcsine · 08-28-2006, 10:52 AM

sorry, hit the wrong button, here is the pic:

PhatA55 · PhatA55's Garage

Yup, you're right. I posted the wrong pic, I'm getting confused about all of the different valves. The first pic is the AAV. It should be this one for the 1982 Decel valve (limiter):

code7rpd · 08-28-2006, 11:03 AM

Number 39 is the part I was referring to and even though mine is connected I have to manually moderate the throttle to keep the car from shutting off.

code7rpd · 08-28-2006, 11:08 AM

Actually I got confused also - it is number 15. How do you go about testing it?

PhatA55 · PhatA55's Garage

Not sure how to test it. I was working on something else and discovered the hoses on the back were split and the PO tuned it to run. As a result, when I replaced the hoses I had your exact problem. I had to reset the mixture and idle to their normal positions to get it running right again. Did this just start or did you fix something else that led to this?

arcsine · 08-28-2006, 11:15 AM

Easiest way is to disconnect and plug the smallest line (shown here as #26 going to the throttle body. On the car, the decel valve will be on the right hand side of the motor towards the front of the car. ) and see if things get better. FWIW, bad decel valves can also lead to high idle conditions.

code7rpd · 08-28-2006, 11:43 AM

I'll give that a try Gary - thanks. The problem just started after getting the control pressures adjusted since they were out of whack. I recently rebuilt the motor and replaced hoses that appeared deteriorated so I don;t think it is a vaccum leak either.

Bobboloo · Bobboloo's Garage

Code7. I think your still confused on the valves. #39 in the top picture is the AAV (aux air valve) #7 is the AAD (aux air device) also called decel valve.

In the next picture #49 is the AAV and #15 is the decel valve.

The top picture is for 81' and earlier. The bottom picture is for 82' and later.

What year is your car?

It sounds like your decel valve may be leaking. It's function is to keep RPMs from dropping to fast, causing the motor to stall when you take your foot off the gas.

Testing is done with the engine warm. Note the RPMs at idle.

Remove the hose leading to the decel valve from the throttle housing and seal the hose and connector on throttle.

Now start the motor (still warm). If the RPMs change then the valve is defective. If they stay the same then the decel valve is fine.

code7rpd · 08-28-2006, 12:14 PM

My car is an 81 but looking at the pics my vacuum diagrams look closer to the picture for the 82. I'll take a closer look when I get home. The part I am thinking of looks like the last valve in the phot that was posted by Gary.

code7rpd · 08-28-2006, 05:30 PM

Bobby, I checked the valve and there was no change in the rpm's so I guess I can rule it out.

Mysterytrain · 08-29-2006, 06:08 AM

The AAV is the saucer shaped guy [part 49] on the 82 PET diagram. Its function is to provide a big glup of air when the engine first cranks. Engine vacuum then seals it off and it should be out of the picture. If it leaks you will have a high idle.
The AAR is the bugger with with the electrical connection. It provides a high idle when the engine is cold and then slowly closes as the heating element heats up. It should also be out of the picture once the engine reaches operating temperature. This guy can fail in an open or closed state. It can leak and the heating element can fail. The easy way to test it is to pull the outer hose off when the engine is cold and see if it is partily open. You will need to use an inspection mirror. Reconnect the hose and get the engine hot. Turn off the engine, pull the hose and look again. It should be closed. If it is not check to see if you have 12 volts at the connector. If you do then you can pull the part and clean it or fix it.
AAR Revisited
I'm not clear on your problem. Does the car stall when its cold or is it stalling regardless of engine temp? The AAR is suppose to keep the rev's up and prevent the stall when the engine is cold.
The Decel valve is designed to prevent the RPM's from dropping like a brick when you lift off the throttle. You might have a vaccum connection that is missing from it. Look at the connection in the 82 drawing above. The control connection is the small nipple on the left side that goes to the throttle body. That might be the problem.
What is the idle speed when the car is warm?
Additionally, your car has the Lambda computer/ oxygen sensor and frequency valve all of which are attempting to control the mixture. You might want to have a look at this website:
http://members.rennlist.com/jimwms/CIS/CIShome.html

code7rpd · 08-29-2006, 06:34 AM

The car stalls when hot. If I let it idle and I hit the gas, it drops to the point that the alternator light flashes and the car either dies or gets close. When driving it will shut off unless I ride the clutch and feather the throttle. I looked at the decel valve yesterday and did not see or feel a small nipple or hose going to the throttle body. It looks like the decel valve is behind the fuel distributor and it has one large hose connected on the back. I will take another look to see where the hoses connected to it go.

arcsine · 08-29-2006, 08:02 AM

On the post-'80 CIS cars, the intake system should look like this:

The picture is of the backside of the motor, as if you were in the backseat and did not have the firewall in the way. On the far left of the picture are the AAV and decel valve with the AAV on the bottom and the decel valve just above and inside it. Both valves have two large fittings on the inside and only the decel valve has the smaller nipple fitting on the outside.