924Board.org

WildP1 · Joined: 25 Dec 2020 Posts: 18 Location: Switzerland

Hi all

I adjusted the fuel mixture today so that all exhaust values are to spec. It runs and idles nicely when warm at around 1000rpm or so. It's an early 1976 Porsche 924.

But when I start it when the engine is cold it idles at like 700rpm and there is black drops of something coming out of the exhaust. I assume it runs too rich during cold starts. When I rev it slightly it obviously doesn't rev as nicely as when it's warm and also drops below 700 before going back up to around there after letting the throttle go.

It has a new fuel pump, fuel accumulator (one 40cc instead of two 20cc), injectors, filters, a rebuilt fuel distributor, new plugs and pretty much all of the ignition system is fresh.

Any suggestions as to what it could be?

I was thinking maybe it's smth to do with the WUR, the AAV or the CSV.

Thanks a lot.

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

Mine is the same, but revs fine even when cold.
WUR is indeed the issue in my case, keeps mixture too rich when cold.
_________________
Supercharger and EFI kits
https://www.the924.com

Fifty50Plus · Posted: Tue Jul 19, 2022 6:46 am Post subject:

Black drops are soot (from exhaust system) covered water vapor. Not to worry.
_________________
1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

safe · Joined: 18 Mar 2017 Posts: 698 Location: Sweden

If it runs good when warm, just live with it, its kjet and its old...
_________________
/Magnus, Stockholm Sweden
=======================
Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

ChrisMadge · Joined: 16 Dec 2020 Posts: 29 Location: Bristol, UK

Eliza · Posted: Tue Jul 19, 2022 9:56 pm Post subject:

Guys guys... just because your cars are old ( vintage?

) doesn't mean they can't be made to run properly.

WildP1, if your warm idle is at 1000rpm and your cold at 700, check your Aux air valve for proper operation and adjust it ( yes that's possible within certain boundaries).

Fast cold idle should be slightly higher than warm, around 11-1200, and settle to around 900/950 depending on MY after a few minutes.

Eliza
_________________
1985 924 NA RoW
1981 931 S2 RoW

WildP1 · Joined: 25 Dec 2020 Posts: 18 Location: Switzerland

Eliza · Posted: Thu Sep 08, 2022 4:42 pm Post subject:

Search for "adjust auxiliary air valve"- loads o threads out there.

Here's a good one:

https://www.fiatspider.com/f15/viewtopic.php?t=39810

I usually first dump a cleaned AAV in the freezer for an hour to see how much it opens, then into hot water to see if it closes properly. I then adjust the 7mm nut so it closes completely at around 70 deg. C.

This is obviously not an exact thing but usually works well.

Good luck,

Eliza
_________________
1985 924 NA RoW
1981 931 S2 RoW

WildP1 · Joined: 25 Dec 2020 Posts: 18 Location: Switzerland

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Smoke test for vacuum leak
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

WildP1 · Joined: 25 Dec 2020 Posts: 18 Location: Switzerland

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2595 Location: MI

Dribbling injectors at low flow? Poor spray pattern?
_________________
80 Turbo - Slightly Modified

WildP1 · Joined: 25 Dec 2020 Posts: 18 Location: Switzerland

Eliza · Posted: Fri Sep 09, 2022 4:08 pm Post subject:

If you can smooth out your cold idle with the throttle, I would still suspect your AAV - that's actually its function. Creating a controlled air passage while cold to incrase metered air, and thus fuel. Actually, my cold engine idles at around 1200 with how I set my AAV and drops to 950 within a few minutes. Remember that the AAV ( like the WUR ) are not only heated internally but also by the warming up of the engine via their contact surfaces.

I wouldn't guess your WUR is the cause here.

For vac leaks, let the engine idle and spray brake cleaner all over the engine bay, you'll hear the pitch change when there's a leak. Also try around the injectors and all the hoses.

Your AAV may be outside spec, even at the full level of adjustment. If you can, borrow another one and see if it makes a difference.
_________________
1985 924 NA RoW
1981 931 S2 RoW