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924-UK · Joined: 14 Nov 2023 Posts: 25 Location: UK

Still having a few issues starting from cold. She fires up straight away and revs, but then dies after about 10-20 seconds even when trying to modulate the throttle. It does this until there is a bit of heat in the engine and then runs OK.

I have tested all elements as per Haynes (CSV, AAV, WUR & TTS). The only issue I couldn't figure out was the supply to the AAV - my test lamp flashes when cranking but I figured this should be a constant supply to close the valve after a few minutes? Haynes isn't too clear on this.

Any help appreciated.
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'84 924 2.0 NA

Raize · Joined: 18 Sep 2013 Posts: 337 Location: Scotland

If it's revving just for a moment after starting (using the extra Cold Start Valve fuel) then struggling for the next 10-20 seconds before dying, then the mixture is too lean for some reason.

AAV wouldn't effect that (all intake air is metered) so it has to be a WUR issue or sticky plunger in the fuel distributor.

My 924 was doing the same and for some reason it runs properly with my K-Jet tester installed, but has the lean-start issue if I connect the WUR line as it should be connected. Hard to diagnose but it could be either somehow air bubbles in the WUR line are effecting the operation, or the small tube has collapsed internally and is restricting flow.

924-UK · Joined: 14 Nov 2023 Posts: 25 Location: UK

924-UK · Joined: 14 Nov 2023 Posts: 25 Location: UK

Update ... it's taken me nearly a year to get to the bottom of this, but a previous owner had rebuilt the WUR and installed the heating element upside down! No wonder it was running so bad at startup.

So it starts on the button now, with no throttle.

As an added bonus, my hot start issues have also gone.
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'84 924 2.0 NA

fiskolja · Joined: 08 Aug 2024 Posts: 18 Location: Malmö, Sweden

Nice one!
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924 NA 1977

coup85 · Joined: 12 Aug 2024 Posts: 54 Location: Madrid

Beartooth · Joined: 05 Apr 2022 Posts: 280 Location: Roberts, MT

I'm guessing it was the whole arm? So the WUR wouldn't work right, or maybe wouldn't do anything at all: it'd make sense because it would start off the cold start valve, then want to die because of not enough cold enrichment. I can't remember if just the heating element could be removed and turned around, but if so, I'm not sure just that would make a big difference. It's probably a place where a fuel pressure gauge would be helpful: anything wonky with the WUR is going to show up in the control pressure. Nice little Easter egg from the previous owner, regardless.
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1980 931 diamond in the rough