Hesitation when engine cold - any ideas?

[fairzy]

I’ve had my RS4 for about 6 months so far and aside from some large bills (Michelin Pilot 4s all round, deflapping / stage 2 at MRC etc) I love it.

I’ve noticed that until the engine has warmed a bit (water gauge has started moving) the engine can stutter / doesn’t accelerate cleanly under partial load but if you put your foot down it’s fine. I mentioned it to MRC who couldn’t find anything.

I’ve since run VCDS and it had a ‘left engine mount solenoid valve N144 P1573 - 004 - open circuit intermittent’ fault but don’t know if its linked.

Can anyone help?


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[Pistolpete2543]

The engine mount solenoid will be unrelated, that's just telling you your engine mount is worn.

Could be the SAI system, think it's common that this stops working. Or possibly MAF sensor. Could be tricky to diagnose straight away, might have to systematically eliminate things.

[andyg72]

Mrc stage 2
I assume it’s de flapped this could be the cold running issue

Mines not great when cold
Perfectly fine once warm

Edit just re read de flapped



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[demon8991]

I have the same issue with mine as well, exactly the same symptoms as you describe.

I got the car in November and the previous owner said it did it for the 2 years he owned it too.

Will be watching this thread.

[fairzy]

Mrc stage 2
I assume it’s de flapped this could be the cold running issue

Mines not great when cold
Perfectly fine once warm

Edit just re read de flapped



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I’d read that deflapping could cause this but it was like this before the work was done.


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[fairzy]

The engine mount solenoid will be unrelated, that's just telling you your engine mount is worn.

Could be the SAI system, think it's common that this stops working. Or possibly MAF sensor. Could be tricky to diagnose straight away, might have to systematically eliminate things.

Thanks Pete. How would I start to diagnose the SAI system / MAF? Wouldn’t VCDS pick this up?


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[Wavey Dynamicist]

I have the same problem too..

I am thinking it could be worth getting the injectors cleaned, or looking at cleaning/replacing the MAF sensor.. Like you, there are no related codes logged..

Approaching it logically,the nature of the problem suggests to me it's a combustion issue which would draw my attention to fuelling/ignition.. Given that i just had the engine carbon cleaned i would assume the intake air is nice enough quality and it has 8 new spark plugs so i can rule that out - the symptoms of the issue (heat related) also would rule out coil packs to me..

An interesting one for sure.

[marc1]

Injectors? Fuel pump?

[fairzy]

I have the same problem too..

I am thinking it could be worth getting the injectors cleaned, or looking at cleaning/replacing the MAF sensor.. Like you, there are no related codes logged..

Approaching it logically,the nature of the problem suggests to me it's a combustion issue which would draw my attention to fuelling/ignition.. Given that i just had the engine carbon cleaned i would assume the intake air is nice enough quality and it has 8 new spark plugs so i can rule that out - the symptoms of the issue (heat related) also would rule out coil packs to me..

An interesting one for sure.

That is interesting - I also had a carbon clean done within the last 1k miles and it’s due an annual service in 2 months so was going to change the spark plugs thinking that might help and could also get fuel filter changed .

MAF was next on my list after that. Can you clean the injectors?


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[Wavey Dynamicist]

I have the same problem too..

I am thinking it could be worth getting the injectors cleaned, or looking at cleaning/replacing the MAF sensor.. Like you, there are no related codes logged..

Approaching it logically,the nature of the problem suggests to me it's a combustion issue which would draw my attention to fuelling/ignition.. Given that i just had the engine carbon cleaned i would assume the intake air is nice enough quality and it has 8 new spark plugs so i can rule that out - the symptoms of the issue (heat related) also would rule out coil packs to me..

An interesting one for sure.

That is interesting - I also had a carbon clean done within the last 1k miles and it’s due an annual service in 2 months so was going to change the spark plugs thinking that might help and could also get fuel filter changed .

MAF was next on my list after that. Can you clean the injectors?


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You can clean injectors yeah, just gotta remove them and take them to a company who offers the service, shouldn't be hard to find and from memory costs about £20 an injector.. I just haven't got round to it yet.

Let's keep the thread up to date as things progress!

[JamesBaby]

Coolant temperature sensor and Maf is what I’d be looking at.


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[Wavey Dynamicist]

Coolant temperature sensor and Maf is what I’d be looking at.


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What's the reasoning behind coolant temperature sensor?

[JamesBaby]

It affects fuelling based on engine temperature.




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[FaisalJ]

This is common behaviour for a deflapped car - mine does it too (and I too thought something was wrong and asked MRC to check).

As to why it did this before - are you sure your flaps were operational? They can get stuck.


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[Wavey Dynamicist]

It affects fuelling based on engine temperature.




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That's interesting i didn't know that.. Seems to read ok on the dial but it would be good to confirm with a digital read-out.. Problem is, with no error codes and without putting a thermocouple on the coolant circuit you've got no way to tell if the sensor is off..