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kye · Posted: Thu May 27, 2004 11:07 am Post subject: setting the idle

in trying to debug some cold weather issues i'm having, i've gotten to the stage where i'd like to adjust the idle, but a look through the Haynes doesn't reveal the setting, or if there is even such an adjustment..

before I "give up" and spill my guts on here asking for help debugging i'd like to see if this a) is possible, and b) helps any..
i'm relatively new to mechanical work, and am trying to do as much by mysefl as I can..

it's a 1981 931, UK delivery car..

thanks!
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it's funny, but when they said "Anything is Possible", that's exactly what they meant....

Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

There should be a sticker under the hood that gives the setting. On my 81 924 the idle is 850 rpms. The idle can be adjusted by turning a screw that is inset in the throttle body. Turning the screw clockwise lowers the idle and counterclockwise raises the idle. I am not sure if any of this applies to a 931 though.
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1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

kye · Posted: Thu May 27, 2004 4:29 pm Post subject:

excellent.. i'll have a look for that and report back.. at the moment it's trying to idle 600RPM on (what sounds like) two cylinders. i'll see if I can get it to idle at 900RPM on two cylinders!

_________________
it's funny, but when they said "Anything is Possible", that's exactly what they meant....

78porsche924 · Posted: Thu May 27, 2004 5:18 pm Post subject:

You might want to try getting it running on 4 cylinders first, not positive but running on two cylinders might do some damage in the long run. Someone a little more mechanically knowledge would be able to touch on that better.
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90 944 S2
78 924 NA <---now sold and killed by new owner
snailshell trans
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kye · Posted: Thu May 27, 2004 6:08 pm Post subject:

yeah, adjusting the idle is now going to happen a bit later on in the sequence..
I either have electrical problems, spark problems, fuel problems, or vacuum problems. i'll be playing doctor tonight..

_________________
it's funny, but when they said "Anything is Possible", that's exactly what they meant....

924RACR · Posted: Thu May 27, 2004 11:24 pm Post subject:

Well, actually, it's adjusted totally differently on the Series II 931 (81-82) than the 924, at least in the US. I would assume the UK car is the same. The idle (at least in the US cars) is electronically controlled, and so you need to use a timing light to verify the correct setting.

Specifically, the intake air temp sensor is removed (from the manifold) and the hole plugged with a bolt. The sensor is left plugged in, hanging in the engine bay, so that it does not impact the measurement. You then set up your timing light, and as I recall the idle screw is adjusted until the timing mark is seen in the timing window at the bellhousing (under the intake at the back of the engine, more or less directly below the cold start valve). Naturally, once it's set, mixture may need tweaking, iterative process, and when you're all done, the sensor should of course be reinstalled and all back to normal.

Perhaps a Series II 931 UK owner can confirm...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
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Smoothie · Posted: Fri May 28, 2004 8:48 am Post subject:

kye · Posted: Mon May 31, 2004 1:06 am Post subject:

well, progress has been made..

After another read of the haynes, and realising that the idle was only a little low when the car was warm but was *very* low when cold (600 when cold, and maybe 750 when warm) I took out the Aux Air Regulator and inspected it.
In it's cold position it's mostly closed, open about a sixth or an eighth. a search on here revealed someone saying that a third is about right.

So, to test this theory, I installed a copper pipe in the regulators place, and fired it up. It happily started idling about 2500rpm, but must have got the turbo spooled up a bit, and with the extra power, the idle started rising..
I shut it off about 3500, not wanting to test the safety cutouts on anything!

after a few minutes with an axe and a brick (i'm loving being a mechanic!) the section of pipe was pinched in the middle, and had a lot less cross-sectional area. after a few 'tweaks' I constricted it enough to set it to idle at about 1100-1200 rpm, which seems to work well, and behaved well in a 25 minute drive I did with it in place.

once i've sorted out a few other problems i'm having (i'm pretty sure I have a vacuum leak somewhere, and I haven't checked the timing yet) i'll revisit the regulator I have and if it's still too restrictive but still closes after 5 mins, i'll look at filing/drilling the plate in it so that it is a bit more open when in it's cold position. worst case is I stuff it up and have to buy a new one, which I would have done anyway, so no harm in trying..

i'll keep you all posted, even if it's so you can read about it and think "he did what to his car???"

_________________
it's funny, but when they said "Anything is Possible", that's exactly what they meant....

Smoothie · Posted: Mon May 31, 2004 2:56 am Post subject:

Are you gonna do something with the aux air reg and put it back in?
I had mine out for a look inside almost 10 years ago, so I don't remember details of it, but there was some way of adjusting the opening - whether by bending something or adjusting a screw. Like I said, I don't remember exactly, but there was a way.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

kye · Posted: Mon May 31, 2004 11:47 am Post subject:

yeah, i'll put it back in once i'm done, as i'd prefer to have the idle time go slower once the car has warmed up.
I didn't see any way of adjusting my unit, but i'll have another look.. was it a screw type adjustment? or something else? that would be the optimal way of fixing it!
_________________
it's funny, but when they said "Anything is Possible", that's exactly what they meant....

Smoothie · Posted: Tue Jun 01, 2004 10:38 am Post subject:

I had another look at my AAV today and it all came back -
Looking at the long squarish part of the AAV you should see on one side toward the end, a round plug/cover and on the opposite side, a smaller round recessed piece. The smaller round piece is the end of a rod and the bi-metal bar assembly inside is mounted to it. Adjusting involves driving that rod in or out. Looking at the end of the rod at this point, if you were to drive it inward, that would be closing the air passage more. If you want to have the air passage opened more, the plug/cover has to be driven out the other side, then the rod driven back from there, but before you do anything, get a measurement of how far down the rod is located in case you want to put it back the way it was, later. Anyway, to have the passage opened more, the larger plug/cover has to be removed. That's done by driving in the rod from the other side to its' limit of travel. Once that's done, the plug/cover will be sticking out about 6-7mm. You have to remove it the rest of the way however you can, but carefully because it forms a leak proof seal (to prevent a vacuum leak). Once that plug/cover is off, you'll see the end of the stud that goes into the several times previously mentioned rod. So, to have the air passage more open at cold startup, drive the rod in by the end of the stud. To have it more closed, drive the rod in from the other side (the flat, normally exposed end of the rod).

-But before you bother with any of that, have a look at the air passage opening - should be -roughly- 1/4 open at room temp. Then throw it into a freezer for 15 min. and look again - should be maybe 1/2 open (I'm judging by what mine did in a freezer that's set to about 10*F (-12*C)

) Then hook it up to 12v power and see that it closes - mine took 10 minutes to close completely. If it doesn't open/close as it should, remove the 4 screws and have a look inside. The spring-loaded plate with the odd-shaped hole cutout should rotate easily on its' pivot by finger pressure and return when you release it.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Smoothie · Posted: Tue Jun 01, 2004 2:21 pm Post subject:

Driving the rod in. This part of the procedure looks the same whether you're just moving the rod slightly to adjust the air passage to be more closed or you're driving the plug/seal out the opposite side.

The plug/seal after being driven out ~6-7mm - needs to be carefully removed from this point so as not to mess up the seal it provides.

Driving the rod back the opposite way by the stud&nut end. This is the way to go to open the air passage more -

Interior view with the rod driven fully in by the flat, exposed end.
In this position the air passage would be less open at startup and would close sooner on warmup.

Here, the rod was driven fully in the opposite direction (by the stud&nut end).
In this position the air passage would be more open at startup and would stay open longer during warmup.

Checking the rods' depth. The reading taken previously and being shown here is 0.15" (3.8mm). I later adjusted it to 0.10" (2.5mm) to have it opened a little more, hoping this will take care of an occasional problem with stalling during warmup in cold weather.

Quick summary of moving parts -

Reassembly -
Make sure the side of the bi-metal bar and the "tab" on the rotating plate meet up..

...which should leave it at a position similar to this -

....then rotate it to line up the screw holes -

_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

kye · Posted: Wed Jun 02, 2004 11:24 am Post subject:

thanks for that smoothie, that's a huge help.
i'm familiar with adjusting things (computers, audio gear, etc..) but the adjustments on cars seem to be very different. so different that I don't even see them!
the pin on mine appears to be pushed in a fair bit, which would explain why it's quite closed. i'll knock it out and push it back a ways and then adjust it to taste.

mine doesn't have screws to open the unit, they appear to be pins, but that's a side issue as I can still adjust it and see the gap without opening it..

thanks again!

you guys rock

_________________
it's funny, but when they said "Anything is Possible", that's exactly what they meant....

Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

Smoothie
Mine looks much different, perhaps the part changed in 82.

Kye
I belive that the pins you refer to are rivets. You can drill them out and sinply buy a rivet gun at the local hardware store to replace them.
_________________
1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

Smoothie · Posted: Wed Jun 02, 2004 1:09 pm Post subject:

Cool