I have a 1976 stock FI 2.0 with 128,000 miles on her. ive had the car 2 months and have gone thru her pretty well because im a stckler for knowing where im at with my Porsches. I have replaced all vacuum hoses points, plugs , adjusted valves and timing is dead on. I live in Indiana so its not been cold yet. My car runs fine after she warms up but does not run well at all until then . She idles but going through the gears she surges pops and farts for about 5 to ten minutes of run time then she runs great. are the 914's usually this cold blooded. I dread to think what it will be like when it starts getting chilly out. Am I expecting too much? I just feel im missing something. Thanks for all imput

Is the AAR working?

Im not sure How do I check it?

Take it off and blow through it then touch it to ground and the wire to + for a few minutes and it should close "after warm up"!

This was taken from Rennlist.com info sheets

Function: Provides additional air to the engine during warm-up to overcome drag due to internal friction of a cold engine.
Normal Value(s): about 14 ohms of resistance from the connector to the body of the unit.
Failure Modes
Stuck open: Fast idle. Check by removing input hose to the regulator after the car has been running for 10-15 minutes. If you feel suction on this line, the regulator is stuck open. See below for rebuild and rejuvenation procedures.
Stuck closed: Poor running (low idle) after cold start. Check on cold engine by removing the input hose immediately after starting. If you do not feel suction, the regulator is stuck closed. See below for rebuild and rejuvenation procedures.
Broken heater lead or heater coil: Engine stays at fast idle for a long time after starting (more than 10 minutes). Check by removing the regulator and grounding the case and applying +12V to the input lead. In a few minutes, if your heater is working, you should feel the base of the AAR getting warmer - eventually, it gets quite warm. If the lead is broken where it enters the AAR, you're out of luck. It is actually insulated through the crimped connector into the AAR - a really crappy design, as it's easy for the insulation to break down and short it, or for it simply to break off due to stress from handling. If it's broken right at the connector, you may be able to salvage it by rebuilding (see below)
Shorted heater lead or heater coil: Check this if you blow the 25A (red) fuse on the relay board every time you try to start the car. See below for rebuild procedures.
Notes: The regulator is open when cold, and closes over time as a heater inside the unit (+12V supply) acts on a bimetallic strip. The opening inside the AAR has a slot that starts off wide and gets narrow. The idle stays high while the wide part is open (~3-4 minutes), then drops off as the narrow part remains exposed (~10 minutes for fully closed). Even if the heater is non-functional, the engine heat will eventually close the regulator. Because the regulator is no longer available new or rebuilt, you will have to obtain a used unit or repair your own unit - you are on your own here!
Does Yours Close Too Fast?: If you'd like for the AAR to stay open longer, try adding 2.5 ohms (four 10 ohm/10W power resistors in parallel) in series with the heater. This will reduce the heater power from ~14W down to ~10W, and cause the AAR to close more slowly. Should add a few minutes to the fast idle part of the cycle. Please exercise caution - that resistor pack can get hot, make sure it is safely secured.
Rebuilding and Rejuvenation: These things are NLA and working units don't show up for sale very often. I recently sacrificed a frozen unit to figure out the best ways to revive them and/or rebuild them.
How does it work?: First, you have to understand how the AAR works inside. Click here to see a diagram of its guts. It's not so clear from the diagram, but the way this thing works is that in the top part of the unit, there's a cylinder with a slot cut in the side. The cylinder is open on the top, and rotates in the bore of the top part of the body. When the cylinder rotates, the slot moves past the opening in the side, so that air flows from the top port, through the open cylinder, through the slot, and out the side port. When the slot rotates away from the side port, air flow is shut off. The cylinder rotates because it's driven by a shaft on the bottom, that has a bimetallic strip connected to a slot cut in the bottom of the shaft. The other end of the bimetallic strip is secured by a screw to the body of the AAR. It's adjustable so that the AAR can be temperature calibrated. In the bottom of the AAR is a heating coil that warms the bimetallic strip when the car is running.
Rejuvenation: This is your best bet, if your heater is still working and the lead is in good condition. AAR's are exposed to all kinds of muck in the airflow path, and are often stuck. The bimetallic strip can't provide very much torque to turn the shaft, so the cylinder has to move freely in the bore. Remove the AAR from the car. Turn it upside down and flush the side port with penetrating lubricant (e.g. WD-40). Flush, flush, flush, and flush some more. Plug the top port, fill it up with penetrating lubricant, and let it sit upside down for at least a day. Clean it out, flush it a few more times, then try again. If it still doesn't open and close, repeat the procedure until you tire of doing it and give up, and proceed to the rebuild procedure.
Rebuilding: This is NOT a guaranteed process, take this on only as a last resort. Your first challenge is to get inside of the AAR. This is not an easy task. I have heard that you can "pop" the top of the AAR off by jamming a large round screwdriver in the side port, securing the base in a vice, and levering the top. Personally, from my tries at doing this, I suspect that you will instead break off the side port, and/or destroy the guts when it comes flying open, or chop you hands to pieces. Your call, several people have told me that they've done this and it works, I couldn't get it to work for me. An alternative procedure is to take a Dremel cut-off wheel (please use safety glasses, and perhaps, a full face shield), and to very carefully go around the perimeter of the flange on the body and cut it off, so that you're removing just the top part of the flange (it should form a ring). Your goal here is to leave a shoulder of the flange, so that you can epoxy the top back on when you're done. Good luck.

Assuming you're successful and haven't been fatally injured by this process, remove the top. You should see the ceramic insulator with the heating coil in the bottom of the unit. If yours is in good shape, DON'T TOUCH IT. Put it aside. If your heater lead is broken or your heater is burned out, you have to remove the ceramic part completely. I don't believe you can do this without destroying it, because the ground pin and the heater lead pins are riveted through. Before proceeding, try to open the crimp that's holding the heater lead on the bottom of the AAR as much as possible, so the wire can slide through. You can get the ceramic heater out by inverting the unit, then using an awl or a punch to punch-out the center rivet. Rip it all out and toss it. You will be replacing the heater with three small 5 ohm, 5 Watt rated, wire wound resistors in series. Arrange all three in the bottom of the unit, and secure them to the base with epoxy or JB weld. One end goes to the ground pin in the base, the other goes to a wire that exits the AAR through the port in the bottom. Set aside. BTW, I HAVE NEVER DONE THIS - Dave Darling said he did it and it works.

Next step is to get the cylinder freed up. If yours is really stuck tight, you will probably have to remove the top port to be able to extract it. First, mark the angle of the top port to the top assembly of the AAR with a marker or a piece of tape. Clamp the top, stick a round screwdriver into the top port, and lever it off the top of the AAR. You can press it back on later with a vice and peen the edge to make sure it's secure. You should now be able to see the top of the cylinder in the bore when looking in where the top port was attached. Below, you'll see that the bimetallic coil is held on by a small screw. Carefully mark the exact position of the slot where the screw is attached - this is the temperature calibration position, you'll need to attach it later to this exact spot. Remove the screw, and pull off the bimetallic coil, the other end is engaged in a slot in the shaft that drives the cylinder. Soak everything in penetrating lube - the shaft, cylinder, etc. Next, you'll notice a small pin in the shaft, that limits the rotation of the shaft, and that must pass through a key slot in the body of the AAR if you want to remove the cylinder. Stick a flat end screwdriver in the slot in the end of the shaft, and GENTLY try to turn the shaft. Won't budge, right? OK, here's what I did. Invert the top and gently tap on the bottom of the shaft with a hammer a couple of times. Not too hard - you'll break off the pin. Now, turn the unit back over, find a small round end tool (I used the butt of a scredriver), and use it to tap the cylinder back down into the bore. Repeat this process until you can start to turn the shaft. Once you can get it to rotate, move it to the position where the pin is lined up with the slot, and then drive it through, and remove the cylinder. You'll find the bore is full of rust and muck. Keep cleaning, lubing, and testing the cylinder in the bore until it moves with almost no effort.

Reassemble, I would press on top port AFTER I put the cylinder back in, but BEFORE, I put the bimetallic coil back on. Make certain you DO NOT use the shaft of the cylinder for a pressure point, push from the body of the unit with a vice. Peen the top to hold it in place. Reattach the bimetallic coil to the exact position you marked when removing it. Use high-temperature epoxy to form a complete seal between the top and bottom of the unit, and wait 24 hours before testing to make sure the epoxy is fully set. Congrats, you should have a fully-functional AAR!

wow, thats a lot of words. Does it idle at about 1800 rpm when cold then go to normal idle after about 5 minutes?

Luckly I didn't have to write them!!

Thats why I put the first short line at the top for a quick test!

The car idles right at 900 to 1000 upon start up . I am going to check the AAR this morning . I will clean it up and lube it .

The AAR has strong vucuum pull upon cold start up Any other ideas ?

Where does it idle after warmup?

It idles right at 1000 rpm It is the smoothest at that rpm ive set the ecu to where the idle is stable and not hunting . its set at about 4 clicks from the richest setting .

Ok, so if it has strong vacuum at start up, then it's never closing. Needs to come out and soak for a bit. There are plenty of procedures for it. Whats going on then is you basically have a vacuum leak all the time. the car was re-tuned for this leak, richening up the mixture to make it run. When it's cold, the ECU is already making the mix rich, thats why it's coughing on you. You will need to get the AAR working, then re-tune the ECU and idle to get it correct again. Cold start ~1800 rpm, then ~950 when warm.

He said it has a strong vacuum upon cold start up. That is normal. AAR closes off upon warm up. Sounds like something with the CHT to me. Check the cold and hot readings of the CHT lead to ground. Cold about 2000 ohms, warm about 100 ohms. You will need to unplug the CHT to do this reading.
Tom

I pulled the aar and have it soaking. it was stuck half way open . I freed it up and now giving it a good soak. Ill reinstall tomorrow and see how it does.

Yes, but if it's open, he should have high idle, he does not. So the car was re-tuned for a stuck open AAR.

Yep, that could be it.
Tom

I reinstalled the AAR and noticed no change The slide moves freely now but appears to be half open . The slide is between the smaller slot and wide open . Is this normal or should it be wide open ? the engine still has a start up idle of between 1000 and 900 .

Check Brad Anders 914 D-Jetronic parts and troubleshooting info. Directly relates to your symptoms.
( After starting when the engine is cold, the idle doesn't come up while the AAR is open and AAR has been checked for proper operation, and idle performance is good after warm up.) = Cold mixture is too lean/ cold resistance of the CHT is too low.
I think there is a link to his site here somewhere. Yep, at top of home page/914 info/misc 914 sites/ Brad Anders.
Tom

Yep

Sounds like a CHT problem

Do you have the proper one in the car.

There are wild differences, and my car runs a little rough in the first minute on the proper 017 CHT

The 012 runs well at the start, but after warmup, hunting problems and too rich.

017 is proper for my car, but the 270 Ohm resistor does not seem to make a difference.

John

I replaced the CHT sensor with the stock unit . Maybe its the wrong one . I got it from AA it was the only one they listed. Does the AAR open wider in the cold as minr is half way the smaller slot and half the wide open slot . Im not convinced that the AAR is fuctioning properly . My CHT sensor had an metal extention piece on it that the sensor screwd into. the peice was rusty and nasty so I put the sensor in without it . No diagrams showed that it even existed. Maybe I should put it back on perhaps it takes longer to warm the sensor as it must warm up first. the engine was rough upon starting before I changed the CHT sensor . What should the AAR slide valve look like when cold?

The extension piece helps with warm up, it was a add on from Porsche. Put it back on. The AAR does not slide, it rotates in the bore. Basically a clock spring underneath. It should be fully open when cold, and as the spring heats up with electrical power, it closes the AAR. This usually takes about 5 minutes. You should see high rpm at first start, then it will somewhat gradually come down to a normal idle.

I do not have a high rpm at start up its about 1000 and does Idle . Does the AAR open wider when it is actually cold out. Mine is about half open . It does move freely but I am afraid that the spring is not moving it all the way open as that is where it was stuck. I understand these AAR units are difficult to obtain and a PIA to open and repair ?

well, mine used to open around 80 deg that I could remember, and I believe they open all the way at any ambient temp. I never measured the temp they start to close at. I used aero Kroil to loosen mine up, soaked it overnight and it worked like a champ. Even at 1/2 open, your idle should be a little high. I would jump the wire from it to the battery and see if it closes all the way. And a little trick to make sure it's opening, is liquid freeze. Any of those "dusters in a can" held upside down will chill anything enough to test it.

Put aar in freezer for half an hour . It opened wide . I quickly installed it and the Idle went up to 1800 as it should and slowly came back down . I put the extention back on the cht sensor and it made a big difference. the car is still cold blooded but much easier to live with