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.

ovalking · 01-10-20, 07:47 PM

I've experienced this stall issue on my KU engine 100, albeit probably about 6 journeys in the last 20 years! Most of the time it runs great.
I can relate to it happening when you slow down for a junction. Awkward in an automatic!
I had a theory it was something to do with the fuel cut-off but it was never persistent enough to troubleshoot properly.
I hate intermittent issues.

AdrianH · 02-10-20, 03:59 PM

I had a load of trouble with the ISV in my MB, eventually cured when Pete R tracked down a new 'original' for me, the repros we tried were all rubbish. But I had improved the original one no end by putting the 'wet' end in a pot of carb cleaner for a few days and blowing out all the accumulated crud.

Ringmaster · 02-10-20, 06:42 PM

It had its MOT on Wednesday and behaved impeccably.

These intermittent problems are a pain, but I am also guilty of not pampering it as much as I used to, so maybe it does just need a bit of fettling. I have to often remind myself it is 33 years old and apart from plugs and filters, it's all original.

When slowing down at a junction etc., I try to remember to keep one hand on the gear selector so I can slip it into neutral in case a stall threatens. That's one thing I like about the old 3 speed gearbox compared to many newer auto boxes. My daily e46 will only start in park and it doesn't like being put into neutral from drive..

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

12-08-20, 03:40 PM	#3
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,335	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: 1,335	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: 1,335	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.

01-10-20, 07:47 PM	#7
ovalking Grown up member Classic Audi Club Member Join Date: May 2009 Location: Ipswich Posts: 271	I've experienced this stall issue on my KU engine 100, albeit probably about 6 journeys in the last 20 years! Most of the time it runs great. I can relate to it happening when you slow down for a junction. Awkward in an automatic! I had a theory it was something to do with the fuel cut-off but it was never persistent enough to troubleshoot properly. I hate intermittent issues.

02-10-20, 03:59 PM	#8
AdrianH Grown up member Join Date: Jan 2014 Posts: 218	I had a load of trouble with the ISV in my MB, eventually cured when Pete R tracked down a new 'original' for me, the repros we tried were all rubbish. But I had improved the original one no end by putting the 'wet' end in a pot of carb cleaner for a few days and blowing out all the accumulated crud.

02-10-20, 06:42 PM	#9
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,335	It had its MOT on Wednesday and behaved impeccably. These intermittent problems are a pain, but I am also guilty of not pampering it as much as I used to, so maybe it does just need a bit of fettling. I have to often remind myself it is 33 years old and apart from plugs and filters, it's all original. When slowing down at a junction etc., I try to remember to keep one hand on the gear selector so I can slip it into neutral in case a stall threatens. That's one thing I like about the old 3 speed gearbox compared to many newer auto boxes. My daily e46 will only start in park and it doesn't like being put into neutral from drive..