KU engine stalls slowing down when cold

Ringmaster · 07-08-20, 01:57 PM

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?

mikes2 · 07-08-20, 02:43 PM

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.

Ringmaster · 12-08-20, 03:40 PM

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.

Ringmaster · 26-09-20, 05:41 PM

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?

mikes2 · 26-09-20, 09:28 PM

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 ?

Ringmaster · 26-09-20, 09:59 PM

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.

Tun · 28-09-20, 07:13 AM

Check your electrical connection on the ISV. I had a silmilar trouble early this year and the culprit was tarnished copper contacts.

BackintheFold · 28-09-20, 08:34 AM

Was the trouble on your MB? I have a suspicion that my ISV works the same whether connected or not...

Tun · 28-09-20, 09:07 AM

Quote:

Originally Posted by BackintheFold

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.

BackintheFold · 28-09-20, 09:28 AM

Thanks, I'll clean mine out and do the contacts too.

07-08-20, 02:43 PM	#2
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	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. __________________ 1991 90 quattro 20v sport 1991 90 quattro

26-09-20, 09:28 PM	#5
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	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 ? __________________ 1991 90 quattro 20v sport 1991 90 quattro

28-09-20, 07:13 AM	#7
Tun Grown up member Classic Audi Club Member Join Date: May 2011 Location: Buxton Posts: 745	Check your electrical connection on the ISV. I had a silmilar trouble early this year and the culprit was tarnished copper contacts. __________________ 1988 MB quattro 2012 S4 Avant

28-09-20, 08:34 AM	#8
BackintheFold Senior Member Classic Audi Club Member Join Date: Feb 2019 Location: Near an MB ur Quattro Posts: 1,171	Was the trouble on your MB? I have a suspicion that my ISV works the same whether connected or not... __________________ 2006 A3 (daily drive) 1987 MB ur

28-09-20, 09:28 AM	#10
BackintheFold Senior Member Classic Audi Club Member Join Date: Feb 2019 Location: Near an MB ur Quattro Posts: 1,171	Thanks, I'll clean mine out and do the contacts too. __________________ 2006 A3 (daily drive) 1987 MB ur

12-08-20, 03:40 PM	#3
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,326	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.

26-09-20, 05:41 PM	#4
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,326	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?

26-09-20, 09:59 PM	#6
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,326	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.