If you've cheked all your hoses then I'd take the warm regulator off and to clean it giving the super fine gauze a really good going over You need compressed air to do this job..

Hello Folks,

I installed another warm up regulator (used) on Saturday and the car started and drove well for an hour. Yippee! :rock:

Yesterday I took it out again. Started well and stalled as I backed out my drive. :wall:

Had to keep one foot on the throttle while braking to stop the darn thing from stalling. Drove around for 10 minutes and then swapped over my spare ISV. Car fired up well and drove around for an hour without issue.

Today I started it up and it began to stall again within a minute. Again, I drove around for about 10 minutes with my magic footwork. I got home and was about to give up when I thought to start up again and behold, it started and drove well for the next half hour! I'm sure it would have gone on well for the rest of the day.

It seems the car does not get fuel for the first 10 minutes or so and is then fine. Is it the car not sensing the engine's true temperature? I've only a couple of months before the MOT so I hope to solve this soon...

It may seem a daft idea, but is the fuel pump working ok? Noisy, at all?
Fuel pressure is everything, for both injectors, and control pressures.

Thanks Hanuman. The fuel pump sounds OK.

I considered the fuel pump and fuel relay module but I think I would have had a constant issue if they were faulty. As it is I seem to get normal operation after the first 10 mins or so after cold start..

Maybe the car thinks it is warmer than it is at cold start? That may explain why the issue disappears after 10 mins as the temp rises. I will have to look at the temp sender (thermotime switch?) . I think it is located somewhere at the back of the cylinder head.

If it does need replacing I believe I have to drain half the coolant. I wonder if that is strictly necessary?

Looking at 7zap, there appears to be a myriad of thermal switches!

https://audi.7zap.com/en/rdw/audi+10...919-159000/#26

Coolant will flow out when you take the thermotime switch out. If you can find a bolt with the same size and thread you could quickly replace it and only lose a small amount of coolant, or possibly a rubber bung of the right diameter might work to plug it.

If your engine is standard k-jet, then the thermotime switch will only operate the cold start valve and therefore seems unlikely to be the problem. The cold start valve only sprays for a short time on cranking (and a bit longer, maybe 10 seconds, if the coolant temp is very cold). If the switch, wiring or valve was faulty and causing the valve to spray or drip constantly, it can cause problems with starting and running due to flooding. To check this just take the cold start valve out of the inlet manifold, put into a jar with the fuel and wiring still connected and start the car... It should only spray initially for 1-10 seconds or so and not drip / leak after that. If it doesn't spray at all, that is a separate issue which may cause you cold starting issues in cold weather, but wouldn't be the reason for your current symptoms.

I would definitely recommend doing the standard fuel tests - pump volume and injector flow, they're very easy to do - the website "tastes like petrol" gives a good run down of them. Then check your fuel pressures - system, control (cold and warm) and residual. Again all easy to do, you just need a k-jet fuel pressure gauge (easy to make, I did this myself with a guide online for about £30, and you then have that tool at your disposal for future diagnosis as well, I've used mine multiple times now).

Re: pump, it could be failing - fuel demands are higher on a cold engine and so it might be fine providing just enough for a warm engine in a more lean condition but struggles to provide more when needed when the engines cold.

The fuel pump relay if failing tends to cause problems with warm starting and running at first, so less likely to be that I would say.

As the fuel is old, I'd put some fuel injector cleaner into the tank and top up with fresh fuel for a start. Also definitely recommend you clean out the idle control valve as mentioned before if you haven't already - they get all gunked up and can easily be flushed out with carb/brake cleaner.

Just skim read that as I'm on my lunch break...

I serioiusly think you need to removce the warm up reg from the block and carefully rebuild/clean it. It's honestly a very easy job as long as you have a vice with soft jaws to hold the unit steady while working on it as the screws are very tight. Modern crappy fuel seems to react with the gauze or perhaps the bolt that holds it leaveing a weird brown sluge that can only be removed phscically with a pin tipped pick an lots of compressed air.

There is a SS disc that can under some condition's react with old fuel if a car has been left stand for a very long time. I've done two this year and both times it's been sludge in the gauze removal of which has fixed the werid running issues. They were both on old Merc's that had been stood for a couple of years.

If the coolant temp sender fails then the car will simply run a touch rich.

If you take the warm up reg off and send it to me I'll rebuild it for a very small fee.... I mostv aprehensive when doing the first one but I'm pretty confident with them now.

There has been much component swapping and short term fixes. But one aspect that keeps popping up is time. It works for a while after a component has been replaced. Then, it starts being problematic. It could be that from cold, all is fine. What’s the fuel tank level?

Fuel pumps that are struggling can get hot (as with most pumps), and performance drops off.
There may be cause to consider the fuel pump relay. Rough diagnostics- drop a smaller fuse in and see how quickly it blows? It’s really rough diagnostics, unless you’ve got a multimeter to read dc Amps.

Clutching at straws from ¼ world away…

Many thanks for all your input chaps. I can sure use the expertise...

Cleaned the contacts on the thermotime switch with no improvement. The car continued to stall but again, after keeping my foot on the throttle for 5 minutes, the thing began to behave itself. From what I've read above I am barking up the wrong tree anyway.. I'm relieved as I've seen the cost of a replacement and my eyes are already watering after what I've spent on it so far this year..

The fuel tank is half full. The fuel is over 6 months old. I only use E5 super unleaded. I regularly used STP injector cleaner additive, but will do so again and top up. I'm 99% sure the injectors are OK.

I have cleaned the ISV. My mechanic said he ultrasonically cleaned the Cold Start Valve and checked it. Could it still be faulty?

K Simmonds - I might take you up on your offer. The WUR I fit was used. Also noticed no washers on the two banjo bolts going into the WUR. Surely that can't be right?

Maybe the fuel pump is faulty. It's 36 years old and done 96000 miles of pumping.

Can there be many more parts to look at? Could a faulty thermo pneumatic (air intake control) valve be involved?

Will report back asap, but currently juggling work and caring duties.

>>Maybe the fuel pump is faulty. It's 36 years old and done 96000 miles of pumping.

Or the fuel filter is clogged.

When the engine is hot it can function on less fuel.
I'd drain the tank, clear out all fuel filters (pre-pump especially), check electrical connections on pump etc

And a complete fuel system clean from the injectors back.

Also. Other related ideas.
Check the fuel pump electrical supply, and once it’s been running a while, see if you really are getting 12v at the pump. Checked between supply and chassis, and supply and ground line.

Quite a few older cars like my quattro are running an extra relay and supply line due to aging wiring, connections, and even the relays.
Complex relays with a fair amount of internal circuitry. Worth checking for things like bad solder joints- easily remedied with a soldering iron.
These bad joints can easily lead to arcing, which erodes the contacts, so while the relay is functioning, the contacts are getting hotter.

Fuel delivery.
The guideline output from the fuel system was about 900ml in 30seconds. Admittedly, that’s for a WR. I’ve got some notes somewhere for my V8, but it will take a while to dredge them out.