Noise when engine is cold

[rafail7]

When I turn the ignition on and the engine is cold it sometimes idles at 1200rpm which is a lot higher than the usual 700-800rpm and it makes a weird almost like rattling noise but this tends to last about 20-30 seconds and then it goes back to sounding like the car should, anyone know what it could be?

[Cuprabob]

Possibly the Secondary Air Injection (SAI) system which is utilised on cold starts under certain circumstances.

[Mr OCD]

It's the SAI. They are riveted together and the rivets snap ... Causing the noise you describe on cold start.

[froudeg]

The 1.4 TSI does not have a direct secondary air injection system as such...

There are numerous issues with this engine and its twincharger cousin which occur during a cold start:

-A very loud rattle / grinding noise coming from front right of the engine:

This is caused by the camshaft adjuster sticking during startup. Early revision (pre 2011) camshaft adjusters had narrow oil passageways that would easily get gummed up without frequent oil changes, causing them to momentarily stick for a few seconds during startup.
https://www.youtube.com/watch?v=S6L3fF49OT8

-A less loud chain rattle, lasting either a few seconds or minutes, again from the front right of the engine.:

Caused by a faulty / sticking timing chain tensioner. The chain tensioner can fail or stick during cold starts, meaning there is little tension on the chain - a dangerous situation where the chain can slip a tooth or two and end up ruining the engine. Other than changing the tensioner (and chain as a precaution), there is no other solution. Proper oil changes as per service (or more frequent if doing mainly short runs) can help prevent chain tensioner sticking.
https://www.youtube.com/watch?v=EogawKCMfTk
and https://www.youtube.com/watch?v=ZI1i1wk9HIc

-Cold start poor running for 30 seconds or so, making a burbling/popping noise from the exhaust and somewhat rough running (can feel shimmers in the cabin):

Caused by ECU software glitch during pre-cat heating on a cold start. This rough running only occurs on a cold start where the coolant temperature is approximately between 19c and 32c...your dash air temp will closely follow this on a full cold start so can be used as a rough guide of when it will happen. The engine will misfire for 30 seconds during startup under these conditions, making the exhaust pop, burble and rattle with the engine sound rough. It can also occur if you have done a run and let the engine cool down to the point its again in this temperature range and then you restart. There is no solution to this at present as its a fueling issue cause by the ECU, and latest ECU firmware doesn't fix it...as a temp fix if you hear it running rough like this, stop engine and restart - it won't do it again as it won't do the precat heating if the engine has very recently been started.
https://www.youtube.com/watch?v=NZi58oj ... e=youtu.be
and https://www.youtube.com/watch?v=jWxHqyY4BA4

Finally all these engines will make a bit of a diesely like sound on a cold start for 10 seconds or so, and run with high rpm.
This is normal as the engine will overlap exhaust and intake valve timing as part of the process to more rapidly heat the engine up - during this phase it will run at high rpm of approx 1100 and settle down to 700ish after 30 seconds.

Normal: https://www.youtube.com/watch?v=cYiss36Y6pY and https://www.youtube.com/watch?v=VbUOm9WzUPk

Only if the engine is making a particularly loud grinding or rattle noise, that it never did before - should you be concerned. Any diesel like noise during a cold start is normal.

[rafail7]

Okay thanks! I went up to VW today and they're gonna have a look at it next Wednesday and hopefully get it all sorted out