924Board.org

Captain Video · Joined: 09 Jun 2003 Posts: 37 Location: Ft. Worth, TX

My 77' 924 has a problem I cannot seem to figure out. During the summer months the car ran fine. When the weather turned cold the engine will start immediately - run normally for a few seconds, then the engine almost dies - stumbles for a few seconds then surges back to normal running then back to stumble etc... It does this for about 5-8 minutes with less and less stumble each time until the engine is running normally or until the car is warmed up. I can apply throttle when I first start the car and have the revs hold for a few seconds, but then the engine loses power and falls into its run/stumble mode - when I try to apply throttle during the first few minutes of this process (other than at the intitial start as stated earlier) there is no response from the engine at all.

To date I have read up on and tested the "cold start valve", the "thermo switch" voltage at the "cold start valve", removed and checked the auxillary air valve (as per Haynes [Haynes says the aux air valve should have a clear passege through - I have a slit about 1/4 of the diameter of the interior of the valve. When I performed the 5 minute warm up check, the valve closed completely as per the Haynes instructions - should the opening be the complete diameter of the valve's interior????], ohms across the "warm up valve" were as outlined in Haynes, and each of the injectors seemed to be spraying fine. Any ideas on what the problem might be????? I'm at wits end at this point - the only saving grace, is the temperature is beginning to warm up again. Very embarassing sitting in the parking lot at work with an engine stumbling for 5 minutes or so every time I leave work - not to mention what the neighbors think when I am leaving in the early morning.

One other problem is: I have 2 vacuum hoses running from the throttle body to the distributor. When I disconnect either hose there is no difference in how the engine runs - when I put my finger over the throttle body ports I can only feel very slight vacuum on one of the ports even when I rev the engine - not even enough vacuum to have my vacuum guage read. I took the throttle body off and looked to see if the ports were plugged, but both were free and clear. Is this a problem or just a quirk of the 924?

Thanks in advance.

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Have you checked the air sensor plate to make sure it is clean, moves without catching and is properly centered?

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

The opening in the Auxillary Air Valve depends on the temp. Put it in the freezer and IIRC mine opens about 3/4 of the way. IIRC it does not open fully untill the temp reaches 10 degrees F.

The vacuum lines are for vacuum advance and retard. I dont think they would make much difference at idle.

Does the 77 have a temp sensor in the line that runs behind the warm up regulator? I am not sure about the earlier models but if there is one I would test it.

The air sensor plate is a good thing to check although I am not sure that problem would go away after the engine is warm.

I would also do a CIS pressure test. Its possible that even if the resistance is good it may not be working properly.

Try pulling and cleaning one of the plugs. Replace it and start the car let it stumble for two or three miniutes. Pull the plug and see if it looks rich or lean.
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1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

Captain Video · Joined: 09 Jun 2003 Posts: 37 Location: Ft. Worth, TX

Roger and dpw928 - thanks for the information. I will check out the areas you suggested to look.

Roger in regards to the vacuum hoses, that was a seperate issue not related (I think) to the stumbling. I was just interested in finding out if the low vacuum from each of the ports on the throttle body was normal? Do you have a suggestion where I might find a good vacuum source other than the large port to the "power brake" to hook up my vacuum guage to check for any vacuum problems? Thanks

Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

When I check vacuum I use the line that runs to the vacuum switch in the hose that runs behind the WUR. It connects from the switch to the large line that comes out of the rear of the intake manifold. Connect the guage to the manifold not the vacuum switch.
_________________
1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

Check the diagram.
My vacuum lines were a mess. I know the temperature valve will bypass the egr until warm-up #6.
You should only have one line running to your throttle valve from the distributor. If you pull your lines and the timing does not advance they might be wrong.
I got a whole bunch of new hose and started from scratch. It made a big difference. Good luck.

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1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Captain Video · Joined: 09 Jun 2003 Posts: 37 Location: Ft. Worth, TX

Augie Dog,
The distributor vacuum advance on my car has 2 ports one on the front and one on the rear. Both vacuum lines run to the throttle body. I've read in past postings of others on the board that have a similar set up - I don't know the history of the car I have, so I don't know if anyone has put a different distributor in. I think it is original though. I have replaced the vacuum hoses - one of those things that my dad passed along - change the rubber hoses on any used car you purchase! Thanks Augie Dog!

Roger thanks for the input on where to attach the vacuum guage. I will check this out over the weekend. Thanks again!

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

I can't offer help with the vacuum line problem, but your ragged running at warm-up sure sounds like a "classic" control pressure regulator (aka warm-up-regulator) problem. Unfortunatly the only way to definitively confirm or eliminate it as your problem, is with a CIS pressure test kit and gauge.
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'79 Eurospec 931

hexen84 · Joined: 21 Dec 2003 Posts: 24 Location: Detroit, MI

When I first got my 924 I was having the same problem. Mine was caused by the rubber intake boot from the air box to the throttle body. The rubber was rotting out on the bottom. Just a thought for you.

Doodle · Posted: Sun Mar 21, 2004 6:05 am Post subject:

Look closely at augidog's diagram. Every line runs through the vacuum amplifier. Try eliminating the amplifier first. My '77 has the dual diaphram type distributor. One line from the large brake booster line, manifold vacuum, to the rear diaphram on the distributor and one line from the throttle body to the front diaphram on the distributor. This configuration works well for me, but then I have a few other modifications. Try it, too see if it helps. It sounds more like a WUR problem because it only happens when cold but you may not be getting enough vacuum because of your vacuum line configuration to activate the advance diaphram when cold.
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Doodle
Pre 77.5 Mars Red