Engine rattles on idle start up (Video inc)

[halsall1987]

Very recently when I've started the car up and left it to warm up for a minute or so, it feels like the whole engine vibrates and rattles.

It isn't constant, or at any particular rev range. If I blip the throttle it goes away, and does not happen whilst I am driving.

I have had a Custom-Code Stage 1 remap, and was advised at the time to change N75 valve due to boost surge but haven't got round to it yet. It's the n75 that seems to shake the most when it happens as you will see in the video.

Any ideas what could be causing it?

http://i121.photobucket.com/albums/...C-B318-83F384675546-8960-0000052196BB4A36.mp4

 

[aymen_a22]

Do you have any fault codes stored on the ECU? I cant imagine the N75 would cause the engine to shudder like that.

How is the power delivery? You might have a boost leak, I'm not 100% sure though.

Someone will be along shortly to point you in the right direction.

 

[halsall1987]

Haven't had access to vagcom yet, but will definitely run it ASAP. The boost isn't as smooth as it was, the surging is getting a bit worse but I put that down to the N75 needing replacing.

I just really hope it's nothing major internally

 

[aymen_a22]

Might be worth unplugging the MAF while the engine is running to see if it makes a difference.

Doing this will throw an engine code though so make sure you have something to clear it after.

 

[halsall1987]

I doubt its the MAF, as it was brand new less than a year ago. Hopefully its a vac leak somewhere.

When it happens the revs increase slightly to maybe 1500rpm? Any ideas? I think it stops when the SAI stops too.

 

[halsall1987]

Quick bump as I still have this issue:

- Cold start ups causes this vibration (see video) for a minute or two, almost like its the SAI (I'm right in thinking the SAI runs on cold start ups to warm the CAT?)
- When it does this the revs are up 500 from normal and boost is 'feathering' around 15-20ingh instead of 20-30.
- Once stopped the car drives ok, with the odd dip in boost
- There's a wobble on one of the cogs down on the cambelt, I'm due for a change. Is this related?

Thanks in advance

 

[ibizacupra]

often leak related..
cold start SAI should be operating... Is it? sounds like a farting tractor if SAI fan not running but SAI valve open (or stuck open) = airleak pre turbo, post combustion

 

[Ronin225]

Cam chain tensioner, a metallic rattle for 10 or so seconds?

 

[halsall1987]

often leak related..
cold start SAI should be operating... Is it? sounds like a farting tractor if SAI fan not running but SAI valve open (or stuck open) = airleak pre turbo, post combustion

Thanks, yeah farting tractor is a good description! What I mean is that the shuddering happens on cold start ups, as if it is something to do with SAI.

How do I resolve it? Get a smoke test done? Will VAGcom diagnostics give me answers?

 

[halsall1987]

Cam chain tensioner, a metallic rattle for 10 or so seconds?

Not LCR, just LC so I believe belt rather than chain?

 

[Ronin225]

All 20 VT have cam chain tensioner connecting inlet to exhaust cam, is also used as VVT in the later models (circa 2001 onwards)
If the tensioner is on the way out it may have bunny hopped a tooth and timing maybe out causing it to run badly

 

[halsall1987]

Ah ok!

In response to your question then, no metallic sound and it lasts about 60-90s. Stops when the SAI shuts off, which is why I'm leaning toward that as a poss cause.