thinkiwanta928

I've been driving my 81 911 SC daily for a two months now. Really a lot of fun. Now that I have the outside mirrors adjusted where the lights of the SUV or truck behind me doesn't blind me. I also am wearing yellow lens glasses to calm the glare down of headlights coming towards me.

Upon cold start up, and the air temperature here has been in the 40Fs lately, the engine idles around 1,800 for about one minute, and then drops to 1,100. I allow it to idle for about another 30 seconds to a minute for a little more warm up before driving. After driving a few miles or after driving 30 minutes, the idle is back up to around 1,500-1,600. It is not the throttle plate as I lifted the lid yesterday and ensured the throttle was "closed" at idle setting. So that means either I have a vacuum leak, which I doubt because there are times when fully warm and warmer temperature the idle is at 1,000 - 1,100, or it means one of the two air bypass systems is open and allowing extra air around the throttle plate. This is either the auxiliary air valve or the deceleration valve.

When I had the engine out earlier this year to replace the intake box and renew vacuum hoses, etc., I checked the operation of the auxiliary air valve and it was down to just a sliver of a moon showing when heated up with the 12v source on it. My deceleration valve is not connected to vacuum.

Is it possible to pinch of the "source air" of these two devices by reaching around to the back side of the crossover rubber bellows and pinching the large hose that splits into two branches to see if this drops the idle?

Other thoughts?

Many thanks, Charles in Dallas

thinkiwanta928

Update:
I haven't tried to pinch off the hose behind the crossover but that must be where the extra air is coming from since the idle sometimes is at 1,100. If I approach a stop light and don't push the clutch pedal in until the rpms are down around 1,100, the engine will just idle at that point. But if I release the clutch at a higher rpm, the engine wants to idle around 1,600. I wonder if the deceleration valve spring is getting weak?
Thoughts?

stlrj

Your base idle seems a bit high. Try lowering it down to around 800 or so and see if that helps.

thinkiwanta928

So I turned the idle screw in to bring it down. It is now idling between 900 and 1100 depending on.....well, I don't know why it varies. But never too high.
When you guys are driving and let off the throttle, does your rpm drop down to an indicated 300 or 400 momentarily bounce back up and then settle into an idle? Sometimes I feel like it drops so much so quickly it will die. I'm thinking of hooking back up the emission controlling device that slows the drop in rpm for better burning (can't think what it is called).

thinkiwanta928

Bringing this up again. '81 911 SC. My Auxiliary Air Regulator, the device that provides extra air during engine warm up, and then the disc inside should be allowed to pull closed by the spring as the heating element warms up -
I have trouble with idle at 1800 rpm when temperatures are less than 50F. Verified it again yesterday and this morning. On my way to the office yesterday and today with temps in the low 40s here in Dallas. Car won't drop idle to less than 1800. Yesterday afternoon, it was 52F and the idle was around 950. (I screwed in idle control screw yesterday afternoon just to verify the AAR was closed and during driving, when pushing in clutch, engine would die, so I opened back up a little the idle control screw so the engine would not die at intersections)
I sent my AAR off to Fuel Injection Corp and got it back a week or so ago. It is nice and clean and new threaded screws holding it together, but I'm convinced the disc inside is either hanging up on something and not closing or the heating resistance wire is not doing its job when cold.
On the bench, when 60F in the garage, the heating element almost completely closes the disc after 4-5 minutes. I have not bench tested it when device is less than 50F. - Can the resistance wire operate differently in temps below 50 due to age?
My heating element measures 32.4 ohms within spec.
The part number for my device is 0 280 140 218
I have verified 12v at the device while engine is running. I have verified no resistance on the brown wire - ground.
I have called Fuel Injection Corp for some guidance but Robert has not called me back yet.


60F in garage prior to sending to Fuel Injection Corp.

Ohms are to be in the 33 range so this should be acceptable

systemsc

Then you should've just applied 12V and ground and timed how long it took to fully close. It's one of the simplest fuel injection parts on a 911SC to test. Sending is out was most likely a waste of money!

thinkiwanta928

I'm quite well aware I might have wasted $270 getting the device cleaned up and new threads to screw it together. Your comment is stating the obvious. But you also didn't answer my question regarding the resistance wire heating behaving differently in cold weather, such as when less than 50F.

My next step will be to place the AAR in my refrigerator which is about 36F. After in there for a good amount of time to ensure it is very cold, I'll run my 12v wires into the fridge and shut the door. I'll check in in 4-5 minutes to see if the device has moved the door. My guess is it will not.

A few days ago, when the engine was idling 1800 fully warmed up after driving, I pulled off outer hose off the AAR, engine died, and I quickly took a mirror and flashlight to peek inside the device. The moon shaped opening was the same or very close to the same as when the device is cold.

systemsc

The resistance shouldn't change with temperature.

Your $270 charge should've provided a detailed functional report, e.g. over temp, of how the AAR functioned.

thinkiwanta928

Wow! I just received communication back from Robert at Fuel Injection Corp in California. He has build another unit for me, tested, etc. and sending it to me. That is excellent. Thank you Robert!

thinkiwanta928

Yes, That would have been a helpful verification report.
Are you in this business? If so, when I searched repair of this device, I did not find your company as a source.

systemsc

In the 30+ yrs helping Porsche dealers & independents, this is the 1st time someone asked for testing and/or "rebuilding" of a AAR.
The AAR is an extremely simple device, i.e. a resistive heater winding, a shutter, and a spring which controls the position of a shutter.

Check here to see what we do; www.systemsc.com

thinkiwanta928

Great! I like your website. Still not sure how I haven’t found you prior. I also own and improve my ‘76 Jaguar XJ12C (V12 Bosch D-Jetronic). Nice to find someone who can repair its devices.

systemsc

We don't pay Google.

thinkiwanta928

Remember, my problem is the AAR doesn’t close when it is 52F or colder outside, thus a very high idle - 1,700 to 1,800.

I received a replacement AAR
I had both AARs on my workbench and it was about 67F.
My original unit seemed to close the opening at about the same rate as the replacement unit,
however, it never fully closed. Got very close, but I could still pull a tiny amount of air through it, by sucking on the end of the suction side.
(I had my bench top power supply set to 12.4 volts)

I put both units in the freezer and did further testing. (an unrealistic situation as engine running wouldn’t keep the units so cold, but a test nonetheless)
The original unit never closed. It got to about 2/3 closed, but a large air gap still present.
The replacement unit, at 14F fully closed after about 10 minutes.

I installed the replacement unit.
Yesterday morning it was 42F in Dallas and after about 5 minutes of running with 4 minutes of driving, my idle was around 1,050 and after another 5 minutes, it was 950. (Correct)
In the afternoon, it was 65F and it worked properly with my idle at 950.

This morning, it was 48F in my driveway and I ran the engine for about 3-4 minutes. When I shut it down, it was idling around 1,050. (Correct)

Yesterday, Out of curiosity, I tried a couple things to see why the original unit doesn’t behave properly when less than 55F or so outside?
When not heated, my unit measures 32.2 ohms. I heated back up the original unit for about 4 minutes and it was 65F or so in my garage. Then I removed the power and the unit was measuring 32.3 ohms.
I was thinking maybe the resistance was failing when heated and ohms maybe dropping, thus power (heat) output was dropping. Opposite of what an old resistor should do as resistance usually builds with age??.
Then I took the device apart thinking maybe the shellac or whatever was holding the resistance wiring tight on the bimetallic bar was loose, thus not efficiently transferring heat, but it looked very nice.

So I have no idea why it has failed. Certainly don’t think the bimetallic bar has changed its properties. Any physics or EE with thermal dynamics background out there to help?


Everyone likes a little science fair

Original unit hooked up to 12.4 volts in freezer, units about 14F

systemsc

Problem solved, that's great! You did get a refund from having it "rebuilt", right?