924Board.org

[StienbargerR]

Hey guys,

I have decided to set my idle a bit higher, because when the car it warm it idles too low, and the oil pressure gets below one bar.

I just got done reading the Haynes manual, and I read the FAQ as well. Does the Haynes manual make it too complicated? I am a little bit confused why I need a CO gauge and a seperate tach. I don't have seperate tachometer. Can I still set the idle without these things?

If someone can explain it to me, I will do a how-to in the how-to forum, and take pictures as I do it.

Ryan
_________________
1978 924 NA
-250lb lowering springs, Euro Pistons

[Conrad]

Don't go out and buy a tach; the dashboard one is good enough. You don't need a CO meter unless you have very strict emissions laws in your area. The CO meter is most useful for the lamba oxygen sensor system, which your 1978 does not have. There was a good discussion of idle speed and mixture on this board in early February. The (misleading) title was "bosch K jet adjustment." The more authoritative posters in that thread seemed to be "924RACR" and "gohim". Do a search on some relevant keywords or on those user IDs. What I took away from that thread and similar ones is that adjusting the idle and mixture should be done last, after any other faults have been corrected and ignition timing is correct.
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1980 924 N.A.

[Slam]

Conrad's right. One thing I might add would be to check you auxiliary air valve to make sure it's functioning properly. It can cause the kind of idle you're describing if it's stuck or inoperative. It's the small tubular silver gubbins to the pass. side of your intake manifold, near the back of the engine. There's a big air line straight to it from the back of the intake manifold.

HTH
_________________
'84 944 - kid blew motor
'83 944 - resting comfortably. For 12 years
'87 944 - sideswiped by trucker
'80 924 - gone
'78 924 - gone
'77 924 - rusting comfortably

[StienbargerR]

Thanks guys. I found that post.

What is a good way to check that valve?

The reason I think it is the idle is because I think it might have been adjusted when it was not warmed up.

One thing I am confused about- Do I need to adjust my mixture if I adjust my idle?

Oh, Here is one more question, my car's exhaust lets out some dark smoke when I just start it up, or take off from a stop. Could this be a mixture problem?

Ryan
_________________
1978 924 NA
-250lb lowering springs, Euro Pistons

[Benino]

To adjust idle all you need is a screwdriver. There is a screw facing you right on the top front of the throttle body if you stand in front of the car facing the engine. Turn it counterclockwise to increase idle speed.

I don't know how to set the air fuel mixture "correctly" on a car without the 02 sensor system (your car). If you want to play with it you can use a 3mm allen key in the hole between the fuel distributor and the first rubber intake boot to adjust the fuel mixture. I believe turning counterclockwise leans it out and clockwise enriches it.
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1980 Porsche 924 N/A USA
1980 Porsche 924 turbo USA
1987 Porsche 944S USA

[Benino]

forgot to mention, you shouldn’t need to adjust air/fuel mixture when you change idle speed.
_________________
1980 Porsche 924 N/A USA
1980 Porsche 924 turbo USA
1987 Porsche 944S USA

[StienbargerR]

Ok, thanks benino!

I will see what I can do tmr. Maybe I will do a photoshoot too. It is getting paint and body work soon, so I will do a before and after.

Ryan
_________________
1978 924 NA
-250lb lowering springs, Euro Pistons

[Slam]

To check the aux air valve you'll need to remove it. It's attached to the intake by two hex-head bolts. Loosen the air lines, remove the bolts and pull it up far enough to get the connector and air lines off it. Toss it in your freezer for an hour or so. It should open-you'll be able to see through it. Now put power across the contacts on it and leave it for 15 minutes or so. It should close. In fact, it should close somewhat just sitting in the sunlight. If it fails these tests, you could spray some carb cleaner through it and test again, but it's probably on its way out.

Try to avoid changing the mixture until you've ruled out/fixed everything else.

HTH
_________________
'84 944 - kid blew motor
'83 944 - resting comfortably. For 12 years
'87 944 - sideswiped by trucker
'80 924 - gone
'78 924 - gone
'77 924 - rusting comfortably

[ThomasJoseph315]

I'm chasing a bug in my cruising engine speed. Just wondering if you can adjust the idle speed with the air valve. I noticed you can change the time with it too. So where should the screw be when you set the stock 10*? From then I imagine you can set the idle speed, and then set the air/fuel mix. Is there a post anywhere for how and what order you should do all these?

[ideola]

Adjusting the idle with the AAV is not the proper procedure. You should only mess with the AAV if you have the idle adjust screw turned all the way in and the idle is still too high (which would be indicative of a malfunctioning or maladjusted AAV).

Idle speed and AAV opening should have zero impact on cruise. Timing adjustment is also completely independent of idle and mixture setting.

Follow the instructions on your fender well for setting timing. Timing spec is usually based on 2K RPM, so do this first, as the idle speed is irrelevant. Don't worry about tweaking the timing for performance at this point. You want to set it to stock spec so you can dial in the mixture and idle correctly.

Then use a wide band AFR, a CO2 sniffer, or a dwell meter (only works on a car with a functioning Lambda system) to set the proper mixture. Then adjust the idle accordingly. It may take 2 or 3 iterations between mixture and idle to get it dead nuts on.

AFR at idle (950RPM on fully warmed up motor) should be 14.7:1, plus or minus .2 or so. C02 spec is printed on the same fender decal as the timing instructions, so if you're using a sniffer, use those instructions. Just be aware that on cat-equipped cars, it's really difficult to use a sniffer unless you put it in the test port on the downpipe ahead of the cat (should be there on a stock setup, but may no longer be on your car at this point). Do a search on this forum to find the dwell meter method, I don't recall it off hand.

It's important to do all of these adjustments on a fully warmed up car. It's also important to make sure the CIS system is functioning correctly (i.e. a proper CIS test of system pressure, control pressure, leak down, and injector flow test), and to verify that you have no vac leaks. Don't even bother with mixture or idle settings until you are 100% sure you have the CIS and vac leaks sorted.
_________________
erstwhile owner of just about every 924 variant ever made

[ThomasJoseph315]

hold up, let me translate this,.. I was at work earlier on my phone.

So,.. suppose my idle screw is in a random spot. Where should it be when I adjust the timing? All the way out? In? In the middle?

I advanced the timing in my car to 1200rpms then reduced the idle screw. it seemed to give me more power. But I think ever since I did that I may have cause some bucking, perhaps the vacuum advance is kicking in.

I am not sure where to properly set the idle now to put the stock ignition back. Should I just unscrew it? I'm rather confused. I know this doesn't make a bit of difference, but if the idle is one way or the other, I know I have been able to fine tune the timing with it.

[scm924s]

Sounds like confusion reigns!

Timing has nothing to do with idle/mixture. Setting the timing is arranging for the spark to occur at the appropriate point before top dead centre (TDC), this should be set as the factory spec(Haynes) and left alone.

Setting the idle is done with the idle screw on the intake manifold, in conjunction with the mixture screw on the fuel distributor.

Hope that helps!
_________________
1984 n/a Ruby Red Metallic
1988 924S Guards red- sold
1986 924S Guards Red - sold
1984 n/a Black - sold
1980 n/a Le Mans#1 - sold
1980 n/a Le Mans#2- sold
1977 Martini - sold

[ThomasJoseph315]

Hey,

I think I got this thing figured out. So your right and wrong on the timing thing.

So I just got fiddling with the settings and I got the air/fuel mixture to balance out. You can actually hear the difference in the engine. When you get it balanced correctly, it sounds cherry. the next problem was both Air and Fuel where set to high and the timing was set on edge of 10*. Soooo,.. I dialed back the air and fuel at the same time reducing the RPMs still keeping that same cherry sound. Then when I couldn't dial it back any further without loosing that sound I tweaked the timing back a bit to 9*. Basically the high A/F mix was hitting the timing advance and making the car buck on cruising. I think my AAV is still not functioning 100% atm, but as of right now with it warmed up to temp it's running good. I will have to adjust again when my new injectors arrive in a week and after that I'll have to get a AAV I think. The good news is I finally figured out how to tweak this rubrics cube.

YaY!

For those who ever wonder how to set idle and the A/F. Warm your engine to prop temp. Set your engine to 9*. turn the fuel 3mm deally left and right to shudder the engine, find the middle. Then adjust the idle screw to get this cherry sound, it sounds like a properly tuned motercycle without the annoying crotch rocket sharp pitch,.. like when they are sitting at a traffic light, the compression/combustion sounds tight. Where is your RPMs? If they are to high/low you need to raise and lower the idle and fuel trim at the same time to keep the balance and rais/lower the rpms. side note. wait a few seconds between tweaks to let the engine level it's self out. This is nothing you can do quickly.

Happy tuning

[scm924s]

Whilst tuning by ear is a good starting point, you still need to get the mixture set with an exhaust gas test. Not sure how this works in US but in UK this test is a mandatory part of the annual roadworthiness (MOT) test and CO2 emissions have to fall within specified bands. The factory spec(non cat) is about 1.5/2.5% and 2.0% works well on these cars.
_________________
1984 n/a Ruby Red Metallic
1988 924S Guards red- sold
1986 924S Guards Red - sold
1984 n/a Black - sold
1980 n/a Le Mans#1 - sold
1980 n/a Le Mans#2- sold
1977 Martini - sold

[ThomasJoseph315]

That's how it is here too, but I'm not to that point. Yes final tuning will be done with a dyno hopefully this Saturday. Well see tho.