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Strange cold idle - 3200 RPMs

Is this normal? When cold my 78 930 revs up to 3200 rpms for 10-20 seconds then drops down to 2000 then lower where it stays. Is this normal? If not, how to I fix this?
Scott

Old 06-06-2013, 05:54 PM
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scott,

it's your AAR valve [Auxilary Air]. You could remove one of the hoses [going in or out of it] and block 80% of the air by putting something in there.

That way, your car would idle at say 1,200, then return to "normal" after a few minutes. Once your car has warmed up, the valve allowing the air in is completely closed, so it doesn't do anything...

I removed mine completely and use my right foot [accelerator] to add air when cold.

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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 06-06-2013, 06:17 PM
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A couple good reads: How far open should AAV be?

Revs drop slowly when changing gear ... why?
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.

Last edited by mooney265; 06-06-2013 at 06:22 PM..
Old 06-06-2013, 06:19 PM
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thanks... I can do that... assuming I can find the AAR. I'll check in out in the morning.
Old 06-06-2013, 06:40 PM
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Sometimes I wonder if we shouldn't have a 'sticky' on AAR's, since they come up so often. The cheap fix is to put something inside the hose to reduce the amount of air getting in. Or, a small C-clamp or some such device to clamp the hose closed to the degree you want it. Pretty Fred Flintstone, I admit.

The simple diagnostic when seeing super high cold idle is to completely pinch closed the hose leading to the AAR. Your idle should drop down well below 900. If it doesn't, then it aint your AAR causing the high idle.

However, in your instance even though your idle is too high when cold (3200), I find it interesting that the idle eventually drops back to normal when warm (I'm talking 950). That range isn't normal. With that high of a cold idle, it would indicate that the AAR is too far open in its normal range of movement, and conversely won't be closed as much as it should be when fully warmed....which should result in a too-high warm idle as well.

Pull off the hose to goes to it and scope out how far it's open (shine a flashlight into the bore), both when hot and when cold. There should some....but very little....of an opening when she's warm. You can reach inside with a pencil or suitable instrument and forcibly rotate the disc to expose the opening - to get an idea of how much is available. Also check the hose leading from the AAR to the manifold to make sure it isn't a source of unmetered air leaking in.

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Old 06-06-2013, 06:43 PM
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