Classic Audi Technical Mech/Tech Engine » KU engine stalls slowing down when cold

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Old 07-08-20, 01:57 PM   #1
Ringmaster
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Default KU engine stalls slowing down when cold

Folks,

Advice please.....

My C3 Avant is used about once a month on average. It starts and idles fine.
I noticed the brake warning light comes on as I ease her out of the garage and goes off after a few minutes . Classic sign of a weak brake pressure reservoir. Brake pedal seems a little firmer than I remember, but brakes work well.
When I drive off all is fine but she has stalled on me as I slow down/halt.
Once the engine is warmed up this doesn't happen. I have cleaned the Idle Stabilization Valve with carb cleaner. I don't believe there are any vacuum leaks.

My question is: can a weak brake pressure reservoir cause the stalling?
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Old 07-08-20, 02:43 PM   #2
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The brake fault is not causing your stalling. That's a hydraulic problem which does not impact the air fuel mix.

What is the idle speed once the car is warm ? It may be it's on the low side and a small adjustment is required.
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Old 12-08-20, 03:40 PM   #3
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Engine idles around 850.
The problem has not recurred since I posted, so maybe cleaning the ISV helped.
I will just keep my fingers crossed.
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Old 26-09-20, 05:41 PM   #4
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Folks,

My engine is stalling again.

When starting from cold it will not idle. Unless I keep my foot on the throttle the engine dies. So far, after three or four re-starts, the engine then runs properly. Today I drove around for an hour without incident.

The car is used about once a month and I suspect it is the ISV that is at fault, probably needing some adjustment, but I have a question....

I disconnect the battery after each use. Could prolonged periods with the battery disconnected affect the idle stabilization valve's settings?

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Old 26-09-20, 09:28 PM   #5
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There's no ecu on these so disconnecting the battery doesn't reset anything.

You can't really adjust the ISV but you can adjust the control current that it gets. That's by adjusting the throttle body screw. Be careful making changes without testing everything first.

Your timing is I assume correct and in range of the spec ?
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Old 26-09-20, 09:59 PM   #6
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Thanks Mikes2.

It has been a long while since the timing (adj for unleaded) was checked.

I remember around 25 years ago I went through a phase when this sort of thing happened practically every few months after starting from cold. I would get it tuned up and all would be well for a little while before happening again. Suddenly it stopped giving trouble.

Maybe a good ole tune up is what it needs.

Got its MOT on Wednesday, so I just pray it behaves in the short-term, giving me more time to deal with it later.

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Old 28-09-20, 07:13 AM   #7
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Check your electrical connection on the ISV. I had a silmilar trouble early this year and the culprit was tarnished copper contacts.
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Old 28-09-20, 08:34 AM   #8
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Was the trouble on your MB? I have a suspicion that my ISV works the same whether connected or not...
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Old 28-09-20, 09:07 AM   #9
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Quote:
Originally Posted by BackintheFold View Post
Was the trouble on your MB? I have a suspicion that my ISV works the same whether connected or not...
Yep on the MB. When I was getting it ready for MOT it decided it would not idle, you had to keep it alive on the throttle. I thought initially it was the vaccum line to the ECU, which I replaced but it made no difference. I disconnected the ISV to see if it looked dirty and thats when I noticed the blue/green build up on the contacts, cleaned them and bingo perfect idle again.
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Old 28-09-20, 09:28 AM   #10
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Thanks, I'll clean mine out and do the contacts too.
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