SeaDude:
The Bentley SC manual does a fair job of descibing how each item works for our 78/9s. If you give me an address, I will photocopy the material and send them to you.
Keeping in mind that I know next to nothing on this, let me try to paraphrase the manual. The AAV is intended to provide an alternate air flow on cranking the engine. When the engine starts, the AAV is *supposed* to shut off. How? By counter-pressure from a tube that pulls a diaphragm in the AAV shut that had been open by spring load. So, to restate, the spring pressure keeps the diaphragm open, car is started, and running engine vacuum causes diaphragm to shut closed. I suppose if this was not shutting, you would have a lean condition. Leon posted some time back how the "hunting" and "surging" *might* be tied to an AAV that would not stay closed shut, but rather bounces the diaphragm shut and open. I wonder why? Maybe a deteriorated diaphragm or insufficient vacuum from the engine that allows air to continue to bleed into the system.
And yes, looking at the Haynes Fig 11.17 for '79 models seems to show that the hose from the AAV to the engine proper is shared by the AAR, which is a bit downstream.
Like Tbitz, I took my AAR out for a peek and a dosing of WD-40, but stopped short of adjusting it, though that can be done. The purpose of this item is to continue to bleed air into the system during warmup, slowly closing off the air by way of a round disk with a hole in it. The hole is open when cold, somewhere between the two when warm, and then closed when hot (maybe it normally stays open a bit? unsure here). In all events, it is time-related as a current applied to a bimetallic arm attached to the disk cause the arm to move, the disk to turn, and the hole to close. Here again is an item that could easily be bleeding excess air into the system by way of not closing. If you do remove this item, do yourself a favor and slightly bevel the ends of the machine screws. I had a bear of a time trying to get the screws to start threading back in (A/C here, so YMMV). I did note the BEAUTIFUL job Porsche did to machine the area on which this item sits, and the reciprocal machining on the body of the AAR itself: they match up nicely for a, you bet, solid, heat-transferring mating surface. This tells me that Porsche intended ambient engine temp to have some sort of effect on this device.
Whoa, rambled long enough on this one! I'd say in general that if you are running lean it would be good voodoo to visegrip the hose going into the AAR (look for arrow on top of AAR for direction of flow) and the hose going out of the AAV, heading to the plenum.
Jw
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