50 seconds of rattle on startup

[alecw]

Hi,

Car is a 2012 2.0 TSI, 101k miles, just bought. On startup from cold, for about 50 seconds the RPM goes to about 1200, then settles back to 800. During this time, there is a rattle from the offside of the engine that goes away once it drops to 800 RPM.

Any thoughts on what this might relate to?

Many thanks,
alec

[Cuprabob]

It's normal for the idle to increase to around 1200rpm for a short period after a cold start up. With regards to the rattle, does it re-appear if you increase the revs to 1200rpm using the throttle? If so check things like the bonnet stay, engine cover or heat shield as they are common causes of rattles.

If only happens on start up from cold it could be the timing chain or tensioner.

[alecw]

Hi,

It doesn't rattle after it's dropped down to 800RPM, even if you push the RPM up afterwards.

Is the timing chain or tensioner something that is supposed to be replaced every X miles/years, or are they supposed to last the life of the engine?

Thanks,
alec

[Cuprabob]

In theory, the timing chain is supposed to last the lifetime of the engine but the reality is that they can stretch. Also, on older EA888 engines, which yours is, there were issues with tensioners and the design has been revised many times. If you do a search on this forum you'll find out more detailed information on the subject.

[Cuprabob]

I can't remember if the 2.0 TSI uses a Secondary Air Injection (SAI) system or just runs a specific map to heat the cats up on cold start up for a brief period but if it has a SAI pump, it could be that rattling as that would only be running during the higher idle speed fime period. Hopefully somebody else can confirm.

[alecw]

Thanks for the info. The noise actually stops a few seconds before the revs drop - hopefully it's audible here, the dropoff is about 45-50 seconds after startup:

https://youtu.be/Jni7unv31gM

alec