911SC idle question

Rich Lambert · Rich Lambert's Garage

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

Superman · 02-24-2003, 07:22 AM

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.

Rich Lambert · Rich Lambert's Garage

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

Rich

BlueSkyJaunte · 08:03 AM

Auxiliary Air Regulator. I think.

re: AAV and Decel Valve

Rich Lambert · Rich Lambert's Garage

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

Gunter · Gunter's Garage

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

john walker's workshop · 02-24-2003, 04:52 PM

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.

tsuter · 05:46 AM

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!!

Jdub · 02-25-2003, 07:04 AM

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

Rich Lambert · Rich Lambert's Garage

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

tsuter · 02-25-2003, 10:20 AM

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?

tsuter · 11:42 AM

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.

Superman · 02-25-2003, 10:40 AM

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.

10:58 AM

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.

tsuter · 11:16 AM

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?

tsuter · 02-25-2003, 11:21 AM

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.

Rich Lambert · Rich Lambert's Garage

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

Rich

tsuter · 02-25-2003, 11:35 AM

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.

Superman · 02-25-2003, 12:24 PM

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.

tsuter · 02-25-2003, 01:41 PM

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.