924Board.org

[sermeussteven]

Hello guys,

I encountered some other problems today. My 924 NA from 1979 is starting, running and idles at about 1000 rpm just after starting.
From that point on, the rpm's steadly increase...After a few minutes the rpm passes 1500 and so on...
The idle screw (at the throttle housing) is half a turn away from the minimum.

My first thought was the WUR but fuel pressure is 3.7 bar in the system and stays steady. (I have no valve on my tester so i cannot measure the closed pressure)
The accumulator is probably broken because the system is not maintaining the pressure long (+- 30sec)
Since the system pressure is within acceptable limits for a warm engine, my best guess is to rule out the WUR and auxiliary pressure regulator from the possible causes?
The only problem with ruling out these two is that I don't know what else can cause this over time...
Any ideas?



Side question:
Where is the relay for your radiator fan located? Beneath the dash, bottom row, the 3th on from the left?


Many many thanks in advance!!

Steven

[kingzetts]

Steven,
That sounds like a problem with the auxiliary air valve to me. I had this problem years ago on a K-Jetronic 911 which had the wrong AAV fitted. This valve allows extra air to bypass the throttle flap when the engine is cold, and closes under the action of a bimetallic strip as the engine warms and no longer needs the extra air. If your valve is not closing, this could I think lead to the idle speed increasing. Or, if the wrong AAV for the car is fitted, it may allow too much air through when part-warm, which would cause increasing idle speed during warmup but then normal idle once fully warm. To check, locate the AAV and clamp the hose either to it or from it and see if that causes your idle to drop.
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John,
1980 924 turbo "timewarp" being restored

[Rasta Monsta]

Are you saying control pressure is 3.7 hot or cold? If so, your WUR is not functioning, and someone adjusted the idle air bypass to get the car to idle while cold.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[sermeussteven]

I checked the air valve, it is fully closing. So it doesn't look like the problem is there...

The second guess was right, with or without de wur connected makes no difference. Fuel pressure is always 3,7 hot or cold...
So the WUR is probably blocked... Strangly it has no trouble starting cold or hot...and if so, i should be able to get a normal situation with the idle screw after a while because the engine is hot. But the idle screw is already at minimum. Any sugesstions?

Now what i noticed today is even more strange. As long as i don't touch the throttle, the rpm stay steady at 1000 rpm. Even if the engine is completly warm If I then tap the throttle, the rpm doesn't return to 1000 but stays at like 1500.. Even if you put a load on the enigne to recude the rpm's it returns to 1500 as soon as you take the load away...
However if you switch off the engine and start it again, it is again at 1000 rpm...

Does anybody has any idea what is causing this?

[Ozzie]

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