924Board.org

[caswah]

Hi!

After surviving a long swedish winter (bless snow chains) it´s about time to do some relaxing driving, without grasping the steering wheel until white-knuckled thanks to icy roads..

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Here´s my problem:

Car starts quickly and nicely, idles at around 1100 (turned it up a bit) BUT
after about 20 sec it starts dropping and after 45 sec from start it´s down to 400RPM or even beneath the scale. 400 RPM=rough and shaky idle.
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It does not stall/stop but I don´t want to risk it doing so if Im in a crossing, about to turn onto a big road or so.

Before this it was last run five weeks ago w/o problems. Made no changes since. Fresh battery, new spark plugs and brand new spark wires (everything´s 2 months old).

Thought about water in the tank so I added freeze-protection-alcohol (whatever you call it) which binds water since it´s a waterbased alcohol-solution. No effect.

Cleaned and sand-papered the rotor, distributor cap and spark wires. No effect.

Ideas?
_________________
Euro ´81 924 - Interior being restored

[augidog]

vacuum leak?
Test the spray on your injectors.
May be fuel related if after the cold start injector completes it starves for fuel.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

[alxch1n15]

ive had this problem too. after adjusting the idle, doing it the correct way, its still manages to drop below 500/400 rpm. ive managed to alter the vacuum lines so it doesnt do that. by altering the vacuum lines, i mean that the way i bought the car was not the correct hookup for the vacuum lines. i would start there.

what year car do you have?
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'81 924 n/a

[Porscheaddiction]

Agreed check for Vac leaks...and really take a look at intake boots sometimes if they were not assembled correctly they may not be complete sealed up. Had the problem you had checked all the lines and it turned out to be the intake hoses/boots had a huge 1/2inch opening that could not be seen it was underneath was found by running a finger all along the joint seams.
good luck
Chris.
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1981 924 NA (Restoring mode)
1984 928S (Enjoying the driving season)

[Meneer aard]

My car has that problem to!

When i start my engine the engine idles for arround 900 rpm for a couple of seconds. After that its arround 400 rpm..

When i drive it for a couple of blocks the engine is arround 1000 rpm, I hear a whisper sound or something (just like a turbo) arround 2500 rpm but i checked the vac lines (only one line!?) and replace the intake boot (huge hole in it) but when the engine runs a couple of minutes the engine idles normal. But only 1500 rpm because my fuel pump relay is broken. But when the engine is hot its 1000 rpm.
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Porsche 924 Euro 1977

[caswah]

Thanks for all your answers!

I´m a bit confused about the vacuum lines, in Haynes and other manuals/books there´s a lot of information about the vacuum system, with sketches of six or seven vacuum lines.

I seem to have only one. And there is no such thing as a vacuum amplifier (there should be one in the engine compartment, just in front of the firewall on the right side with a lot of vac lines connected to it).

The one hose I have (?) goes from that round clock-thingy (looks just like the EGR-valve in haynes but Im not sure...) under the distributor cap to the intake manifold.


I will take a look at the hoses and connections to see if there are gaps, but I cant start her up right now since I took out the dashboard for a renovation (take a look at my interior makeover thread if you like).

I have a 1981 euro by the way.
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Euro ´81 924 - Interior being restored

[dpw928]

The vacuum schematics in Haynes are typical for the older 924's with vacuum amplifiers and air pumps. There should be a schematic for your 924 under the hood on the left fender well.

Vacuum leaks, except for large ones, will cause your idle to rise, not drop. Have you checked the other tune up items, like ignition timing, oil change and like spark plugs? If those are OK, reset your idle when the engine is at operating temperature, not cold.

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

[gohim]

Up into the 80s models, the EURO 924 has completely different ignition, vacuum and emissions systems from a US market 924.

The Haynes manuals are practically worthless to begin with, and the 80 and later 924 is very different from the 76 924 that the Haynes manual people used to write their 924 service manual.

If your car idles and runs differently when cold or hot, then you have a tuning problem. The odds are you have a vacuum leak, and the idle speed and idle mixture were altered so the car would idle when the engine is cold. Then when the engine starts to warm up, because the car was adjusted to run with the engine cold, no no longer idles properly when warm.

The answer is to correct whatever the underlying maintenance problem is, then adjust the engine to idle properly when warm, and retest when the engine has cooled.

If your Euro 81 924 is has the same ignition, fuel, and emissions systems as a 81 U.S. 924 you should have an electronic idle stabilizer. Late model U.S. 924 cars have very few vacuum lines. The vacuum amplifier has been deleted from the late U.S. cars as well. You should still have vacuum lines running between the distributor, throttle body, the brake vacuum booster, and the vacuum reserve tank in the left front fender. If you do, you must correct/repair all vacuum leaks replacing leaking lines, if your car does not exhibit a stable idle when both cold and warm, AND you must disable the idle stabilizer BEFORE trying to set the idle speed and idle mixture and ignition timing. Otherwise, you will be fighting the idle stabilizer, and you will never get the settings right to have the engine idle correctly both cold and warm.

[tj924]

EIS was only available on US Models, not on Euro.
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TJ
Silver '82 924 NA 5-Speed Manual

[Ozzie]

My car ( and probably most euro as well) has this setup for vaccuum.

_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[caswah]

Many opinions, thanks to all!

As I mentioned I cant start up right now since my I took my dashboard out, but I´ve found a leak in the rubber housing (that big 5inch-diameter-hose) that connects to the throttle body. Just like "Porscheaddiction" said. That might be it, but I´ll see in a couple of days when I put the dashboard back.
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Euro ´81 924 - Interior being restored

[Benji0301]

I have the breather hose which runs from the crankcase breather to the spigot on the air filter housing but I do not have any restrictor. Is it internal in the hose? & how much does it restrict by?

[Ozzie]

Its in the hose near where it joins to the block.
If its blocked run a 5mm drill through it.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Benji0301]

I must have the wrong hose fitted because theres no restrictor in the hose that runs from my crank case brether to air filter box. I ordered what I beleived was a new crankcase breather hose from German Swedish & French & i was sent the actual breather itself. I have no idea on how to remove the old one or fit this one. It looks like a press in fit but I don't know? Can I just machine an adaptor to restrict the hose & just push it in the hose? Anyone got an idea of the restrictor size? I beleive I read somewhere here that it is 13mm but not sure?

Cheers

Dale

[Ozzie]

My hose crumbled to pieces and a new hose from Porsche was $130.
F**k that!
I used some normal hose and I had a piece of urethane the right size with a 1/4 inch hole in it. Fitted with gasket silicone and works fine.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance