924Board.org

[nrwheele]

I've been trying to go through my '81 924 N/A to resolve a few lingering problems, and I encountered something (possibly) strange while replacing some vacuum lines. There was what appeared to be a vacuum line cap in one of the hoses leading to the throttle body, specifically here:



Removed the hose, with the cap left in place:



When the plug is in place and the hose is on, the engine seems to run normal (minus the issues I'm hunting down now) - when the plug is removed and the vacuum line is reattached, the tach jumps to around 2000+ at idle.

My knowledge of vacuum systems is minimal, but I feel like NOT having a plug here would be essentially like having a vacuum leak, since it's basically routed right to the air metering plate, but it also seems strange that Porsche would have a port here that would capped by default. Is this some kind of test port that is only meant to be open under certain circumstances? Does anyone else have this plugged by default? Or did a previous owner of my car do it to bypass some kind of vacuum leak elsewhere in the system?

Any pointers would be greatly appreciated!
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1981 Porsche 924 N/A, Black - "Brunhilda"

[Goldwolf]

That line should be attached. Might need to go around all the lines. I changed most of mine with the same rubber/cloth continental hose
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1981 Weissach Edition #179

[nrwheele]

Appreciate the reply! I figured that attaching it is the right move (at least from all the pictures I've seen of other engine bays). I went through my whole vacuum system and replaced all my cloth covered lines with silicone ones, and this find was my only point of contention. The existence of that plug has really left me puzzled, but my car can't seem to be able to run properly without it.
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1981 Porsche 924 N/A, Black - "Brunhilda"

[Goldwolf]

What year is it? Do you have a vacuum line on the distributor?
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1981 Weissach Edition #179

[Paul]

Where is the other end of that hose currently attached? Based on your description, it is probably not correctly installed. Post a picture of your under hood hose routing diagram.
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[nrwheele]

Thanks for all the responses!

My car is a North American Model 1981, Naturally Aspirated.

There are vacuum lines on the distributor

Currently, the line in question connects to a T-joint, which in turn connects to the deceleration valve on the the throttle body and the EEC valve (which in turns goes to the charcoal canister).

Here is the hose routing diagram:


This past weekend, I performed a smoke test and didn't notice any leaks.

If there is any other bits of information that would be helpful, please let me know, I'd be more than happy to provide
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1981 Porsche 924 N/A, Black - "Brunhilda"

[stan_5150]

Does anyone know if the vacuum line routing is the same for the 1978 NA? I got mine started, and runs at idle. But as soon as I try to add power the engine starts to cut out. I'm wondering if I have some lines mis-routed. Thanks in advance.
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1978 924 N/A