Could it be the Cold Start Valve?

Ringmaster · 10-07-23, 11:04 PM

Folks,

My C3 (KU engine) has a stalling problem. It fires up from cold just fine but after about 5 minutes driving it wants to stall if the revs drop below 1000, so I have to keep my foot on the accelerator.

If it does stall it fires up well and a few minutes later the stalling returns.

Could it be the Cold Start Valve? Recently removed and cleaned it. That seems to have solved a poor starting issue I had, but now this. Dizzy cap and rotor are new.

Flipman · 11-07-23, 05:25 AM

Hello.

The cold start valve is only active when the starter motor is in use.
So just a couple of seconds when you cranking the car.

The Warm Up Regulator could be the problem.
Check if all the pressures are correct.

https://k-jet.biz/tests/

/Emil

84CoupeGT · 11-07-23, 07:58 AM

Agreed it won't be the cold start valve. The warm up regulator is a possibility as Flipman says and fuel pressure tests (system, control and residual) are definitely worth doing. Also worth checking for vacuum leaks.

Other possibilities include:

Idle control valve (if your car has one - small cylinder with electrical connection, attached to the rubber boot near the throttle body). These get gunked up over time and cause idle problems. Very easy to remove, spray carb cleaner in and watch all the muck come out!

Another possibility is debris in the fuel tank building up somewhere (e.g. fuel filter) and causing a restriction, however I think this would be likely to become obvious when there were higher fuel demands from the engine rather than at idle.

Could also be an electrical issue such as a bad connection on the coil, hall sender (connector on the distributor), or ignition control module. These type of issues often only become apparent when the car gets hot.

Incidentally, are your new dizzy cap and rotor Audi or Bosch parts? I recently had an issue with a new rotor arm on my Coupe, after only a couple of hundred miles the rotor (which was aftermarket - JP Group) starting losing spark through the bakelite to the distributor shaft. Took me ages to work out what the problem was! The symptoms were different (hesitating and misfiring which got progressively worse until it conked out completely and wouldn't restart), but worth knowing as the last thing we all suspect is often new parts!

Keep us posted!

AdrianH · 11-07-23, 08:49 AM

I once had a similar problem –*strted fine, but after a few minutes running very rough etc. Turned out to be nothing more than a temperature sensor in the head being slightly loose, and (I'm guessing) not telling the coldstart injector to stop firing once the engine had started to warm up.

ovalking · 11-07-23, 09:16 AM

I had this issue intermittently on my KU, but the problem seems to have gone away with a replacement fuel pump relay.

There is a function relating to fuel shut-off (which I don't fully understand). If this is not working quite right the relay could shut off the pump and cause a stall in certain situations.

It is easy to check - replace the relay with a jumper wire between the two big slots, and see if the problem goes away.
Do not leave it like this - as the pump will run all the time the ignition is on. Safety hazard.

Ringmaster · 11-07-23, 10:49 PM

Thanks Chaps,

Rotor is Bosch and dizzy cap is Intermotor. That seems to be OK. ISV swapped over and issue remains.

I didn't think a faulty Warm Up regulator would have such a symptom. Hmmmm.

I will keep you posted.... May be a while though.

Hanuman · 17-07-23, 04:33 PM

If it was one of my cars, I’d be looking at cleaning hoses and throttle bodies. Oily residue accumulates.

Eg, quattro.
During the warm up phase, the car will get extra air via the auxiliary air valve, which contains a sliding valve plate. As it warms up, the valve closes, and the car runs by the metering set with idle screws, etc.

The narrow bore hole gets gummed up, leading to complete starvation eventually. Usually arriving at a roundabout with a stalled engine…

Ringmaster · 17-07-23, 08:47 PM

[quote=
The narrow bore hole gets gummed up, leading to complete starvation eventually. Usually arriving at a roundabout with a stalled engine…[/QUOTE]

Where would that narrow bore hole be, Hanuman?

Hanuman · 18-07-23, 02:51 PM

I’m not familiar with your machine, but it’s where the idle screw is, which would be on the throttle body/butterfly. I’d look at 7zap, but it seems a bit flakey these days…

https://audi.7zap.com/en/rdw/audi+10...5/1/133-37000/
My guess, item 35.

I did mark up a drawing, but we don’t have the tapatalk plug-in working on the forum at present, so I can’t post the image

ps. The drawing is based on a 1984 KU, with 5cyl engine, with a variety of K-jet. I think. I’ve no idea if that’s actually correct.
pps. Is this a continuation of the previous issue? http://www.classic-audi.co.uk/forum/...ad.php?t=39843

Ringmaster · 18-07-23, 08:59 PM

Quote:

Originally Posted by Is this a continuation of the previous issue? [url

http://www.classic-audi.co.uk/forum/showthread.php?t=39843[/url]

Thanks Hanuman. It's a 1987 KU. Yes, it is a continuation of the previous thread although most of those issues (rough idling, hunting, intermittent stalling) seem to have been resolved by replacing the dizzy cap and rotor arm and cleaning the Cold Start valve.

As the current issue so far seems to occur after about 5-10 mins driving I suspect something is stopping fuel getting through once the Cold Start valve has done its job.
The engine otherwise runs/sounds just fine.

I'm looking at the Warm Up Regulator and Fuel Pump Relay next. The petrol is 8 months old super unleaded, but I doubt it's the fuel. I've had older in it before.

17-07-23, 04:33 PM	#7
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,010	If it was one of my cars, I’d be looking at cleaning hoses and throttle bodies. Oily residue accumulates. Eg, quattro. During the warm up phase, the car will get extra air via the auxiliary air valve, which contains a sliding valve plate. As it warms up, the valve closes, and the car runs by the metering set with idle screws, etc. The narrow bore hole gets gummed up, leading to complete starvation eventually. Usually arriving at a roundabout with a stalled engine… __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

18-07-23, 02:51 PM	#9
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,010	I’m not familiar with your machine, but it’s where the idle screw is, which would be on the throttle body/butterfly. I’d look at 7zap, but it seems a bit flakey these days… https://audi.7zap.com/en/rdw/audi+10...5/1/133-37000/ My guess, item 35. I did mark up a drawing, but we don’t have the tapatalk plug-in working on the forum at present, so I can’t post the image ps. The drawing is based on a 1984 KU, with 5cyl engine, with a variety of K-jet. I think. I’ve no idea if that’s actually correct. pps. Is this a continuation of the previous issue? http://www.classic-audi.co.uk/forum/...ad.php?t=39843 __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor Last edited by Hanuman; 18-07-23 at 03:15 PM.

11-07-23, 05:25 AM	#2
Flipman Grown up member Join Date: Nov 2008 Location: Sweden Posts: 76	Hello. The cold start valve is only active when the starter motor is in use. So just a couple of seconds when you cranking the car. The Warm Up Regulator could be the problem. Check if all the pressures are correct. https://k-jet.biz/tests/ /Emil

11-07-23, 07:58 AM	#3
84CoupeGT Grown up member Join Date: Nov 2020 Posts: 309	Agreed it won't be the cold start valve. The warm up regulator is a possibility as Flipman says and fuel pressure tests (system, control and residual) are definitely worth doing. Also worth checking for vacuum leaks. Other possibilities include: Idle control valve (if your car has one - small cylinder with electrical connection, attached to the rubber boot near the throttle body). These get gunked up over time and cause idle problems. Very easy to remove, spray carb cleaner in and watch all the muck come out! Another possibility is debris in the fuel tank building up somewhere (e.g. fuel filter) and causing a restriction, however I think this would be likely to become obvious when there were higher fuel demands from the engine rather than at idle. Could also be an electrical issue such as a bad connection on the coil, hall sender (connector on the distributor), or ignition control module. These type of issues often only become apparent when the car gets hot. Incidentally, are your new dizzy cap and rotor Audi or Bosch parts? I recently had an issue with a new rotor arm on my Coupe, after only a couple of hundred miles the rotor (which was aftermarket - JP Group) starting losing spark through the bakelite to the distributor shaft. Took me ages to work out what the problem was! The symptoms were different (hesitating and misfiring which got progressively worse until it conked out completely and wouldn't restart), but worth knowing as the last thing we all suspect is often new parts! Keep us posted!

11-07-23, 08:49 AM	#4
AdrianH Grown up member Join Date: Jan 2014 Posts: 218	I once had a similar problem –*strted fine, but after a few minutes running very rough etc. Turned out to be nothing more than a temperature sensor in the head being slightly loose, and (I'm guessing) not telling the coldstart injector to stop firing once the engine had started to warm up.

11-07-23, 09:16 AM	#5
ovalking Grown up member Classic Audi Club Member Join Date: May 2009 Location: Ipswich Posts: 271	I had this issue intermittently on my KU, but the problem seems to have gone away with a replacement fuel pump relay. There is a function relating to fuel shut-off (which I don't fully understand). If this is not working quite right the relay could shut off the pump and cause a stall in certain situations. It is easy to check - replace the relay with a jumper wire between the two big slots, and see if the problem goes away. Do not leave it like this - as the pump will run all the time the ignition is on. Safety hazard.

11-07-23, 10:49 PM	#6
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,333	Thanks Chaps, Rotor is Bosch and dizzy cap is Intermotor. That seems to be OK. ISV swapped over and issue remains. I didn't think a faulty Warm Up regulator would have such a symptom. Hmmmm. I will keep you posted.... May be a while though.

17-07-23, 08:47 PM	#8
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,333	[quote= The narrow bore hole gets gummed up, leading to complete starvation eventually. Usually arriving at a roundabout with a stalled engine…[/QUOTE] Where would that narrow bore hole be, Hanuman?