[A3 8P 1.4TFSI CAXC, 125HP, DSG] startup problem on warm days.

[Merimel]

Hello,
Since some time (actually since i bought the car) I'm facing little issue during the startup, but it only occur when specific condition are meet.
There is strange high rev idle, around 1100/min, with shaking a car and really awful sound. It last for about one minute, and then everything back to normal. (see the film below)

This happens only:

• the outside temperature is more than 15°C (trough the winter it start us like a charm - no problems)
• the car is parked for several hours
• It very first turn on after car is parked. If i turn off the car and turn it on again during this first minutestart, problem is gone.

Except that the car runs perfectly, no issues. no power lost. But it's worrying me if it going to damage my engine.

I was to the dealer several times (first they didn't have a clue, checked everything, no fault found,...checked again..)

Spark plugs, oil and filters(all), water pump and timing chain(fully) was replaced during last year.

Obroty zimny silnik - YouTube

Any one is is this something i need to be worried about and what can be reason of this?
Thanks!

-Damian

[Crasher]

Worn timing chains and probably a failing VVT adjuster, a very very common problem. How many Km?

[Merimel]

130 000 km so far (actually is my dad car so it's legit).
Timing chain was replaced about 5000 km ago (January this year, with all the staff - tensor etc.), and there is no, this specific, strange metal rattle sound, and like I said it's happening only during warm weather, last couple of days had pretty cold mornings and car start like a charm.

I was thinking about VVT adjuster, but, correct me if i'm wrong, failed vvt will result in problem during every start, not starts in specific temperature range.

[Crasher]

We had a Golf 5 GT 170 which we fitted a chain kit to but due to the owners circumstances (a very long boring story) we did not fit a VVT unit because at the time FAI or Febi (my two preferred sources for this job) did not do them and at £500 genuine it was more than all the other parts being used x 2! Afterwards it did the usual dry start up rattle that makes the blood drain from your face and then shut up and was fine. By this time we owned the car (told you, long story) and it was being shuffled around and every now and agin would rattle like a bag of spanners at start up, usually after being outside all day in early summer last year. Eventually one of my mechanics decided to buy the car for himself, scrapping his dirty Diesel and getting back into petrol. Obviously he did not want this random rattle so we bit the bullet and fitted a new VVT unit (now available from FAI) and it has been fine since. We did try a new actuator first (I was not convinced) but it made no difference. All the ones we had done since have had a new VVT unit where fitted, not all have them.

[Merimel]

Except replacing it is there any way to verify if it's really a cause of my symptoms? I would not want to pay 500 to replace something which may be fine and still have this strange.

I have read somewhere that this is Secondary Air Injection (SAI) that operates for a short period of time on start up in order to heat the catalytic convertor up more quickly to reduce emissions.
Which make a sense, but I don't think it should looks like this. High revs i can understand but shaking entire car is not healthy imo.

[Crasher]

It is difficult for me to say without directly experiencing it. You can get the Febi version of the adjuster, the 45084, for £275 now but that does not alter the fact that is is an evil task to fit. Do you know if the VVT unit was removed and if the bolt (seen here removed) was replaced with a brand new one?

[Merimel]

Hmm i will need to go to my parents house and look for old parts and invoice, but now, once I saw you pic and checked prices on net, it looks like it was also replaced (VVT). With timing chain, some minor thing were done and I paid ~1000 for everything.

[Crasher]

Do you still have ALL the old parts?

[Merimel]

Hi,
Sorry it took so long, but didn't have time to visit my parent's house this week till today. My dad rid of all old parts some times ago but I've checked invoice and there is position with adjuster.
Anyway I've talked with dad and asked him if he remember if adjuster was there - and he said it was there, so I'm pretty sure it was also replaced.

Btw I found comment that may be connected to my issue -
"Engine Management Unit looks at various temperature and other sensors and decides if it would be safe/worthwhile to pre-heat the exhaust catalyst to reduce emissions. Rather like Goldilocks and the porridge, if things are too cold or too hot the answer is no. If the answer is yes, the idling revs are increased to around 1300 and the ignition timing is considerably retarded. The late ignition means that the gases coming past the exhaust valves are still burning hotly, which raises the temperature of the catalyst more quickly than would happen otherwise. It also makes the exhaust sound wierdly burbly like a diesel. After about a minute, the revs are gradually dropped to normal and the odd noise stops"

Do you think it's valid?

[Crasher]

Yes that is the fast warm up for the cat. It is going to be difficult to help without hearing the noise, how long does it last?