911SC idle question
 

The idle in the '82 SC has been steadily increasing over the past few days (I've only owned the car for a week). This morning, it was 27 degrees out and it idled at 2K all the way to work. Does cold weather affect the idle speed?

Rich

Yes. AT least until she warms up. If that takes forever, then perhaps your AAR is not getting voltage. My AAR is located just above the #5 cylinder head.

AAR? Sorry, I'm not up on my 911SC acronyms...

Rich

Auxiliary Air Regulator. I think.

re: http://forums.pelicanparts.com/porsche-911-technical-forum/97910-aav-decel-valve.html?highlight=aar

This afternoon, in the sunshine, the car idled between 8-12K. So, I'm assuming it just never warmed up this morning. Would it hurt to let the car sit and warm up for 10 minutes in the morning before I take off?

Rich

Porsche does not recommend warm-up idle periods. Maybe a minute, and then driving with low RPM.

tap the air regulator lightly with a small hammer and see if the idle goes down, the next time it hangs for a while. they get sluggish. some folks have managed to free them up with spray carb cleaner. get the idle mixture set properly, as well as the timing and set idle speed to 1000. then you will know where the idle should be when it's hot.

When it is below 30F those AARs often won't fully close on motor heat alone. They require the 12V ceramic heater to work. That may be not working thus the AAR is not closing and keeping your idle high. Easy enough to test.
I do two tests - one is the oven bake test. Put it in the oven and bake at 250F for ten minutes. The other is the 12 V test. Both should close it. Plenty cold here in WI to test these.
I never had much luck peeping into the thing while installed (with or without a little miror) or pinching that big fat hose on the back side. That's how you crack the hose!
But what do I know, I don't have a starter relay in my fuse box either!!

Is there any possibility that your oil thermostat is stuck open? The AAR senses engine temp via its base (note large flat machined base placed square on block) as well as via current fed to a bimetallic strip. If your engine cannot get warm enough the AAR is going to continue to feed air and raise the idle.

Just a thought. I would like to hear if anyone thinks this might be a decent hypothesis.

John

Update...

I was looking around the engine compartment for something to hit with a hammer and found a disconnected vacuum line. It's a small diameter line that goes to the right side (the side opposite of the 2 larger diameter hoses) of the AAV. The line is plugged with a bolt, but the port on the AAV is open. Any idea why this was done?

Rich

If your AAV is for some reason not closing on startup this will also cause a fast idle as air is getting around the throttle just as the AAR is designed to do before it closes.
Couple of questions:
1. Are you saying there is an open hose/line nipple on the side of your AAV away from the two primary air connections?
2. Where is the plugged vacuum line that you found originating?

One more thing to check. If your metal air hose extending off the AAR almost immediately splits into two channels. (Not like in the picture above) then you have a twin AAV install and are using the wrong drawing.
Neverheless if your metal hose is per the drawing above and does not immediately split then the drawing is correct and the prior PO most likley installed the wrong AAV in your car. Only in the two valve AAV setups do you see the third air nipple on the opposite side to the main air hoses on one of them. It would not be left open but would run to the Thermo valve over near the throttle.

Whoa! I'd bet 10:1 that on your car, the highlighted component is the Decel Valve. The AAR is just below it. The AAR is the component we're suggesting to evaluate. The two big hoses should pass air when the engine is cold, and not when it is warmed up.

The reason your Decel Valve is unplugged is because if you plug it back in, your idle will hang too high too long. My car came that way from the PO, and I have tried two or three times to hook it up, and each time I am dissatisfied with the hanging idle. Try it, you'll see. When you unplug it again, be sure to plug the small vacuum line, otherwise it will be a vacuum leak.

Finally, others have said the highlighted device is not a Decel Valve, but rather something else. On their car, maybe they're right. On my car, that's DEFINITELY a Decel Valve and it definitley is annoying until it is disconnected.

clarification on the dual AAV setup:
- are you sure these are really both AAV's or is one the decelaration valve? My '82 has 2 very similar saucer shaped devices & I had assumed the one with a third, smaller diameter, vacuum hose was the decelaration valve?
- I have my engine out at the moment, & have plugged the AAV (the one with only 2 vacuum connections at the back). I have left the second AAV (or deceleration valve???) operational. Is this the right approach.

cheers,
EDIT- Superman just posted & seems to back this decelaration valve identification. My deceleration valve doesn't seem to cause any ill-effects, so I'll keep the AAV plugged & leave the decel valce as it is.

That is correct. The one valve with two connections is an AAV. The second valve (Looks very similar) connected with three lines is the Decel valve.
It is a very common mistake for POs to install the wrong valve in the AAV position. In the older SC, the Dececl valve was very different and you can't make a mistake.
But in the later ones, the two valves look very similar. Except for that third nipple.
So if he is supposed to have one valve - ie., as in the picture above, then someone has installed the wrong valve on his car.
The easy check is the metal air line - does it split immediately off the AAR?

Hey Superman - seems like you need to use drawing 1/7/3 instead of 1/7/2. Then you would have a decel valve that looks like the yellow highlited AAV in drawing 1/7-2.

Yes, I meant AAV. I can't tell where the disconnected hose goes. It goes somewhere behind the engine.

Rich

Can you confirm that the metal air hose does not split right off the AAR. We need to be sure that drawing 1/7/2 is correct for your car as 1/7/3 has a different setup similar to what several folks are describing with similar AAV and a DECEL valve.

TSuter has it right. The unit in the picture is similar, but not the same as my unit. Or yours, Rich. Yours and mine have a small vacuum line. That makes it a Decel Valve. Leave it plugged. Focus on the other unit, just below.

The whole Auxilary Air System with either two (1/7/2) or three components (1/7/3)can cause a fast idle if any leak air.
The AAR is the first to check. The AAV is second. It is normally closed as soon as the motor starts. So if it leaks or sticks open you will get a fast idle. The third component - for later SCs is the Decel Valve (some people remove it). It is normally closed except when a vacuum from closing the throttle opens it to pass air and keep up the idle.
In the ealier SCs (1/7/2) there was also a different looking Decel Valve but it was not part of the Auxiliary Air system. It had its own little loop connecting above and below the throttle butterfly. Some people remove it as well.
Air leaks almost anywhere can also cause your fast idle.
I've seen people get a faster idle just from a can of Techron. In that case everything was so fouled that a little solvent got the fuel flowing again.
The main thing is to test one thing at a time and adjust one thing at a time.

Okay, time for some clarity. Here's a couple of pictures of, what I believe to be, the AAV, with the AAR below and in front of it. You can see the open port and the disconnected hose.

http://forums.pelicanparts.com/uploads/AAV.jpg
http://forums.pelicanparts.com/uploads/AAV1.jpg

Rich

Very interesting. I think someone put the wrong valve in there. They put a Decel valve in where a AAV should be. The clue is the metal line off the AAR does not branch. I don't believe that these two parts are interchangeable. But maybe they are.
In any case if it is a Decel valve installed in the AAV position then it is closed when the motor starts and does not open without a vacuum - and there is none attached. So that is not likley your problem assuming it is always closed. If it is stuck open then it could be.
I would still test the AAR below it first.
Also check that the metal line off the AAR goes around the back to a Y one of which trails back to that valve. The metal line should go to the outside connector on the AAV - not the middle.
As well as leaks in that bolted off vacuum line.
What year is this car?

I saw this is a 1982. I'm beginning to think that someone eliminated the decel valve by back dating the Auxiliary Air System from the 1/7/3 version which you probably had in a 1982 to the 1/7/2 version. In doing so they plugged the vacuum line that used to go from the front of the Decel valve to the throttle body. If you can chase down that line, I would remove it and plug the nipple on the throttle body witha vacuum plug.
They also replaced the metal air hose with the back dated version and then installed the incorrect AAV and it looks like it was installed backwards.
Now the good news is that it may not matter what they did as long as the AAR is functioning OK because the AAV is pretty useless anyway unless it leaks.

It's an '82. So...it sure looks like the blocked off hose goes to the open port. If it was the wrong valve, would that be there?

One more thing...the idle is only high when the car is cold. This lasts the whole 9 mile drive to work in the morning. In the afternoon, it idles about 1.6K for a while and then settles down.

Rich

Yes the Decel Valve and the AAV were in the same area so a vacuum line would have normally gone over there. If it goes around the back to your throttle body you''ll know for sure. It looks to me like the decel valve was removed and the line was then plugged. The AAV however appears to me to be the wrong part and installed backwards.

In any case a fast idle when cold (which it is supposed to do for a while) is most likely the AAR not closing all the way. It should fast idle to 2000RPM+- and then slowly come back as things warm up several minutes would not be nonnormal. Heat transfer is bad when the weather is really cold so there is a heating element inside it. There are two wires to it and possibly the heating element is out or not working thus the AAR is staying open longer than normal until the motor heat or ambient temperature helps to close it.
Your last post seems to indicate that and earlier posts were very on target on how to troubleshoot the AAR.

tsuter, thanks for taking the time to explain to me how this stuff works. Your description of how the AAR functions and possible problems reminded me of John W.'s post.

I tapped on the AAR with a little ballpeen and the idle settled down to a steady 800rpm. I guess this means something's hanging up inside the AAR. Does this thing come apart? If not, where would I spray carb cleaner to free it up?

Rich

It can get gummy with oil fumes etc blowing through and then it sticks a bit. It has a thin sliding half moon shaped metal strip that blocks a hole. I doubt it is effective to spray anything in the hole. I have one out in the shop. I'll look and see if it can be disassembled. I don't believ so. Generally they get replaced.

Well you guys beat me to the punch, but here is what I was typing while I was working.

Glad you are making progress Rich. Tsuter, good call.

------------------------------

When I was experiencing a high idle, I pulled my AAV, and to check if it was closing, I suck (talk about shade tree mechanic, man) on the manifold side of it. If it closes and seals while there is vacuum in the manifold it is fine. My 78SC motor has a system that is similar to what some tried to replicate with your AA system. It should close when the motor is running. All of what has been said is true, bit it could be difficult to a CIS newbee to digest.

As tsuter has indicated, if someone tried to replicate the 78-79 AA system, they used the wrong AAV, but if it is closed when the care is idling, it is not hurting you. The Bentley manual has good pictures and explanations on the subsystems of CIS.

So as tsuter suggested, check you AAR. It is not difficult to remove while the motor is in the car. (Note: You CAN use a flashlight and a mirror to see if it is closing when hot.) After 9 miles of driving in 40 or 50 degree temps here in Illinois, my idle would surely settle to normal. So you AAR my be suspect.

If you remove the AAR, spray carb cleaner into it and clean that sucker out. AS JW suggested early on, this will help if you have crude buildup in the slot of the valve. Repeat until you are confortable, and let it dry before you reinstall it just to be safe (I don't know why). It should be quick. Use some medium grain sandpaper to clean the bottom of the AAR and the mounting surface on the motor. I found that corrosion is possible there, and it will reduce the rate of heat transfer. Aluminum does corrode and crude can build up. May not be all oxidize aluminum though.

Check for voltage on the connector that connects to the AAR. When removing, don't lose that little clip thing. I pry it out wit a very small screw driver and use my finger to keep it on the screw driver. A one hand operation.

It is pretty soilid state. No easy way to open. However you can spray solvent in there and then work the bimetallic spring back and forth in the hole with a screw driver or pencil. You could probably do that while its in the car as well by disconnecting the outside metal hose and pulling it back a bit.
It is not too hard to remove except the AC bracket is in the way a bit. The AAR has only two bolts one on each side in the middle.
These things are also adjustable for when they get worn out enough that they don't fully close when warm. Adjusting is a subject for a separate thread.
My guess is yours is stuck a bit and as JW said often its the easiest things that cause the problem.
Good news that whetver the setup is on your AAV that it is not likely the problem.

Rich-
the deceleration valve is what we're seeing in the photo! Its connected right where it should be (apart from the small diameter vacuum line hanging loose). The AAV is out of sight in the photos but it should be there- its further to the front of the engine compartment (ie. AWAY from the camera) & slightly higher than the deceleration valve, kind of behind the airbox. If you reach your hand back there you should be able to feel it (same shape as the deceleration valve).

Whew! Maybe that solves it. Now all we need is to get the parts diagram 1/7/3 updated to reverse the positions of those valves. Wouldn't be the first time. Hey, even Bentley has the air flow direction wrong on the AAR.
1/7/2 is correct for sure.

I just came in from the garage. I saw the real AAV valve way back behind the deceleration valve and I'm glad I don't have to mess with that.

I took the hoses off the AAR valve and poked a screwdriver in the side that connects to the metal pipe, but didn't feel anything like a spring (it's on the other side, right?). I couldn't get around to the other side. I did start the car up and, at 35 degrees outside temp, it idled up to about 1.5K and then fell down to about 1.1K after about a minute. I can live with that. I may be back if I have to do the hammer thing too often though.

Thanks to all!

Rich

Good news. That means no one tampered with your Aux Air Sytem and the parts are correct. Just use parts drawing 1/7/3 for troubleshooting and remember that the locations of the AAV and DV are reversed. No big deal.
The AAR has a sliding half moon shaped metal gate. It slides across the hole in the AAR closing it off. So when cold, the hole is open. As it warms up the metal gate slides into the hole and slowly closes it. It is activated by the famous Bosch bimetallic strip down in the longer section of the AAR heated by a ceramic encased wire element and the motor itself.
When you stuck the screw driver in there it was open. If it was closd you would bump into the sliding gate. Be careful as it is sensitve. If you can spray cleaner in there then use the screwdriver to manually work the gate back and forth. You can only do this when it is fairly warmed up and mostly closed.
Souk says you can see in there with a mirror but I've never tried that I just take it off to clean as best possible.
Good luck.
There were probably a dozen other possibilities but this is straight forward one.

Does the half moon shaped gate slide from the bottom up?

Rich

If you hold it in your hand and look in the side that has the metal hose attached i.e., air flow would be towards you see arrow on top, then the metal gate slides left to right across the hole to block it. It is activated by the bmetallic strip which is mountd inside the elangated portion and fixed by a metal plug at the end. Since this strip flexes left to right, that is the movement of the gate in the slot.

Like I said in a recent thread, I failed to listen to JW twice, and twice paid the price. Had you taked his advice on the hammer test, you would be days ahead.

Hey, as long as some CIS geniuses are at work here, I'd like to know how in the world my idle goes high when the engine is warmed up, and I've shut it off for a couple of minutes. It would seem unlikely that with all that heat, the AAR would open up. But I am experiencing this phenomenon. Engine warm...normal idle...shut it off for a few minutes and the idles goes high.

What is the outside temp? I have seen this when it is pretty cold ambient. The AAR actually does start to open shortly after you shut down letting in a little air when you next start. The the 12V ceramic pig in blanket heater kicks in and closes it again fairly quick. Until you shut off again - no 12V - it starts to open again. So it is the ceramic heater working - not the heat transfer from the motor.
Lets not discuss adjusting the AAR! :)