Could it be the Cold Start Valve? - Page 5

84CoupeGT · 12-09-23, 10:59 AM

Good point, I was assuming it has the traditional servo. It seems some 1987 C3s have this set up, but 7zap isn't clear which ones. Item 2 in the diagram..

Ringmaster · 12-09-23, 11:45 AM

Quote:

Originally Posted by tractor Dave

Not up on C3 model but have you got a traditional servo or a hydraulic brake booster and bomb?

I've got the hydraulic brake booster and bomb....

See https://webautocats.com/en-gb/etka/audi/a100/73/085100/

tractor Dave · 12-09-23, 01:55 PM

In that case could be your brake booster is faulty. You don't have a vac line to servo on that set up. Faulty booster can cause all sorts of strange issues. It has no impact on engine running other than drawing power from you tandem pump.

Ringmaster · 12-09-23, 06:05 PM

Thanks Dave. I'm worn out with it.

Taking it to my garage tomorrow.. Will advise...

tractor Dave · 12-09-23, 08:48 PM

Don't lose heart. It's bound to be something simple. Are you near West Wales?
I can take a look for you but I'm no C3 expert.

Ringmaster · 12-09-23, 09:21 PM

Thanks for the offer Dave but I'm over in Sussex..

tractor Dave · 13-09-23, 06:26 AM

Sorry I can't help then. You just need the right garage/person to look at it. Old school garage who understand old school cars. Not somewhere who expect to plug it into a computer!

ovalking · 13-09-23, 09:10 AM

Quote:

Originally Posted by 84CoupeGT

Good point, I was assuming it has the traditional servo. It seems some 1987 C3s have this set up, but 7zap isn't clear which ones. Item 2 in the diagram..

Vacuum servo on 4-cyl models only.

ovalking · 16-09-23, 01:13 PM

Quote:

Originally Posted by Ringmaster

Had the emissions checked at my local MOT centre and it was running very lean. CO showed as 0.4. They set it to 3.3 and engine seemed a little smoother. However I needed to see how it did from a cold start.

My last CO test reading was 0.368.
3.3 seems way too close to the max of 3.5.

Ringmaster · 16-09-23, 07:47 PM

Yes, I think so too. It may be the cause of why the engine revs increase for no reason when idling.

Will have to sort that. My MOT is due next month and the MOT chap may kindly adjust it for me.

I considered turning the adjustment screw a little to the left myself, but probably best not to without knowing the exhaust emissions.

Surprised .368 isn't causing you trouble in view of mine had been at 0.4.

16-09-23, 07:47 PM	#50
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,335	Yes, I think so too. It may be the cause of why the engine revs increase for no reason when idling. Will have to sort that. My MOT is due next month and the MOT chap may kindly adjust it for me. I considered turning the adjustment screw a little to the left myself, but probably best not to without knowing the exhaust emissions. Surprised .368 isn't causing you trouble in view of mine had been at 0.4. Last edited by Ringmaster; 16-09-23 at 07:54 PM.

12-09-23, 10:59 AM	#41
84CoupeGT Grown up member Join Date: Nov 2020 Posts: 309	Good point, I was assuming it has the traditional servo. It seems some 1987 C3s have this set up, but 7zap isn't clear which ones. Item 2 in the diagram..

12-09-23, 01:55 PM	#43
tractor Dave Senior Member Classic Audi Club Member Join Date: Apr 2018 Location: Wales Posts: 1,174	In that case could be your brake booster is faulty. You don't have a vac line to servo on that set up. Faulty booster can cause all sorts of strange issues. It has no impact on engine running other than drawing power from you tandem pump.

12-09-23, 06:05 PM	#44
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,335	Thanks Dave. I'm worn out with it. Taking it to my garage tomorrow.. Will advise...

12-09-23, 08:48 PM	#45
tractor Dave Senior Member Classic Audi Club Member Join Date: Apr 2018 Location: Wales Posts: 1,174	Don't lose heart. It's bound to be something simple. Are you near West Wales? I can take a look for you but I'm no C3 expert.

12-09-23, 09:21 PM	#46
Ringmaster Senior Member Classic Audi Club Member Join Date: Apr 2008 Posts: 1,335	Thanks for the offer Dave but I'm over in Sussex..

13-09-23, 06:26 AM	#47
tractor Dave Senior Member Classic Audi Club Member Join Date: Apr 2018 Location: Wales Posts: 1,174	Sorry I can't help then. You just need the right garage/person to look at it. Old school garage who understand old school cars. Not somewhere who expect to plug it into a computer!