924Board.org

[Nein37]

The missing cap on the mixture screw is quite a large vacuum leak. You should plug it with something and see if that helps. When proper mixture is set with the car fully warm, the idle will stumble when the plug to the mixture screw is out. Once you put the screw in to seal up the hole the car should run perfect... if you're mixture is correct.

If you plug up the hole and the car still stumbles at warm idle, the mixture is still off. If it gets a little better but still not quite there, your mixture is probably a bit lean. Give it a tiny turn clockwise and try again.

You need to unplug the oxygen sensor to do this or your FV will just fight the changes you make.
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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.

[CorsePerVita]

[Nein37]

Yes it is a vacuum leak. It is air entering the system after the metering.
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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.

[CorsePerVita]

Interesting. I'll try plugging it this afternoon and see if that helps.
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS

[CorsePerVita]

[CorsePerVita]

Another issue I forgot to mention... the windshield wipers randomly turn on. Sometimes when I turn on the turn signal, other times when I turn. Not always... sometimes. So something is loose or I have a short somewhere.
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS

[ideola]

In my experience, the only way to get the CIS system properly tuned is with a wideband AFR. All of the other half-ass methods I've tried are only good for rough tuning, including the Gunson gas tester I have, the stumble lean / stumble rich method, and dwell meter. So if you don't plan to add an AFR, I would suggest finding a shop with a quality tailpipe sniffer...however, even this may not work because of the cat. There is a test port on the 931 exhaust prior to the cat, which is the proper place to tap in for sampling the air. Either that or replace the stock narrow band O2 sensor (which is probably shot at this point anyway) with a wideband sensor. Most wideband setups have a narrow band emulation mode / wiring setup that you can use to tie in to the stock Lambda system (for proper operation of the frequency valve and the related WOT enrichment...very important!), and you can use the wide band feature for proper tuning of the CIS fuel mixture.

As for the wiper problem, joecitizen did a writeup, I think it's in the how-to section. You should look that over, because it sounds like you're having a short in the steering wheel / steering column / wiper-turn-signal assembly. You don't want to take a chance with this because some of those circuits are (amazingly) unfused, and if they short out, you can melt wires and wreak all kinds of havoc in the big messy bundle of wires behind the instrument cluster. Get after it quick or unplug the wiper harness until you have time to properly diagnose it.
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erstwhile owner of just about every 924 variant ever made

[Rasta Monsta]

Dwell meter method has worked very well for me (it is what factory techs used) but AFR is good insurance to verify boost enrichment and warmup cycle.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[ideola]

Dwell left me significantly rich, AFR revealed that there was a lot that could be dialed in. Out of curiosity, Rasta, have you verified your dwell-adjusted setup with an AFR? I have not gone back to check using dwell since installing the AFR, but now that I think of it, this would be a very interesting set of data to examine...
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erstwhile owner of just about every 924 variant ever made

[Joes924Racer]

You need a wide band afr guage.B-)
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[Nein37]

[Rasta Monsta]

[CorsePerVita]

I hate driving to portland. Mostly in portland. It's a significant reason I rarely go there because the traffic makes me want to punch kittens.
_________________
- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS

[CorsePerVita]

[Rasta Monsta]